Diva Parekh

Portion Summary Sheet

Physics

Topic 1: Measurements

Density (kg/m3) =

A Period of a pendulum = the time taken for one swing (from left to right and back)

Fundamental physical quantities [all other quantities are derived from these}:

[Type text]

20

1. Mass (kg)

2. Time (s)

3. Temperature (K)

4. Distance (m)

5. Electrical current (A)

6. Amount of substance (mol)

7. Light intensity (cd)

Temperature Conversions:

Temperature (C) = 273 + Temperature (K)

Scalars and Vectors:

Scalar quantity = a physical quantity with only magnitude e.g. speed, time, mass, density, temperature

Vector quantity = a physical quantity with both magnitude and direction e.g. velocity, force, weight, acceleration

Topic 2: Forces and Motion

Speed (m/s) = (conversion: 1km/h = m/s)

Velocity (m/s) =

Difference between distance and displacement

Displacement

Distance

Vector quantity

Scalar quantity

Shortest possible distance between final and initial position of an object

Actual distance travelled by an object

Found by calculating the area under a velocity/time graph

Found by calculating the area under a speed/time graph

Acceleration (m/s2) rate of change of velocity

= [-ve acceleration = deceleration]

Acceleration of free fall = 10m/s2

Other formulae

1.

2.

3.

***Acceleration = a; Time = t; Displacement/distance = s; Final velocity = v; Initial velocity = u

Difference between mass and weight

Mass (kg)

Weight (N)

Scalar quantity

Vector quantity

How much matter an object is composed of

The force of gravity that acts on an object

Doesnt change

Remains uniform until within a certain field of gravity but changes when taken out

Property of an object to resist change in motion

Acts vertically downward

Force (N) = mass (kg) acceleration (m/s2) the greater the mass of an object the smaller the acceleration it is given by a particular force

Terminal velocity is when the air resistance is balanced by the weight of an object the object begins to fall at a steady rate [constant speed/no acceleration]

Law of Inertia

In the absence of any external unbalanced force, an object at rest will remain at rest while an object moving at a constant speed will continue moving at the same speed.

Momentum is proportional to inertia. Any moving body will have momentum.

Force (rate of change of momentum)

Momentum (kgm/s) = Mass (kg) Velocity (m/s)

Topic 3: Forces and Pressure

Forces and extension

Length of a stretched spring = original length + extension

Hookes Law the extension of a spring is proportional to the force applied to it provided that the limit of proportionality is not exceeded

Limit of proportionality a point after which the spring becomes permanently deformed and does not return to its original state. Hookes Law does not apply after this point. The spring continues to extend irregularly until it breaks/the breaking point is reached. F = kx [where F is the force and x is the extension].

Elasticity is a property that implies the ability of an object to regain its original shape on removal of the force deforming it.

Plasticity refers to the ability of an object to retain the new shape gained due to the deforming forces acting on it.

Moment of a force

Moment of a force (Nm) = force (N) perpendicular distance from pivot to force (m)

Turning force needed is the least when the force is furthest from the pivot and at a right angle to it.

During equilibrium/Balanced beam

Total clockwise moment = Total anticlockwise moment

Total weight = sum of all forces + weight of the beam itself

Contact force = Total weight

Centre of Mass the point in an object where it behaves as if its entire mass is concentrated around a point

If a pivot is placed at the center of mass there is no movement.

A weight causing a clockwise moment is always balanced by another weight causing an anti clockwise moment.

Pressure

Pressure is the force per unit area acting perpendicular to a surface

Pressure (Pa or N/m2) =

Pressure in fluids (Pa or N/m2) = Height (m) Density substance (kg/m3) Gravity (N/kg)

Gas Pressure (Boyles Law)

Pressure (Pa) Volume (m3) on condition that Temperature (K) is constant

[where k is a constant]

The volume of a fixed mass of gas is inversely proportional to its pressure, provided its temperature remains constant.

P1V1 = P2V2 [Provided temperature is constant]

[Provided pressure is constant]

[Provided volume is constant]

***P = pressure; T = temperature; V = volume

Mercury Barometer

Used to measure atmospheric pressure: consists of a long glass tube (80cm) filled with mercury and inverted into a trough (done carefully to prevent air entering). The length of the mercury column is proportional to atmospheric pressure.

Atmospheric pressure at sea level = 1.01352 105

Manometer

Functions using the same principle as barometers: used to compare difference in pressure of two gases

Contains a U-tube holding a fixed amount of a certain liquid (generally mercury density = 13.5 g/cm3 OR 13534 kg/m3)

When the gas supply tanks contain the same gas, the liquid is at the same level in both sides

When different gases are placed into the tanks, the gas with the higher pressure pushes down on the liquid

The difference in pressure can be found using the difference in height of the liquid columns on both sides using the formula for pressure in fluids (height is found, density of the liquid and gravity is already known)

Topic 4: Forces and Energy

Forces (Newtons or N) cause changes in motion or shape of an object

Types of forces

Friction opposes motion

Air resistance/Drag is the force of friction when an object moves through air or water

Upthrust is the upward push of a liquid or gas on an object

Weight is the pull of gravity of an object:

Weight (N) = Mass of object (kg) Force of gravity (N/kg)

Force of gravity on Earth = 10N/kg

Contact force is exerted by a surface and opposes weight

Resultant Force is the single force that has the same effect as two or more forces

Centripetal Force acts towards the center of a circle on a body moving in a circular path (a force acting on a moving body at an angle to the direction of motion, tending to make the body follow a circular or curved path)

Joules (J) is the unit of energy

Forms of Energy

Chemical Energy is energy stored in chemical bonds of compounds. It is released when they are broken down. It is found in fuels, batteries, and in the human body.

Kinetic Energy is the energy possessed by a moving object. It can be found by the formula:

K.E. = [K.E. = kinetic energy (J); m = mass (kg); v = velocity (m/s)]

Gravitational Potential Energy is the energy stored in an object above the earths surface (or generally can be taken as any surface). It is the energy that causes objects to fall down. It can be found by the formula:

G.P.E. = mgh [G.P.E. = gravitational potential energy (J); m = mass (kg); g = gravity (N/kg); h = height aboveground (m)]

Electrical Energy is the energy transferred by moving electrons in a circuit. It is a good way of transferring energy since it is easily converted to different forms.

Nuclear Energy is the energy stored in the nucleus of atoms that is released when the atom is broken down or split. Radioactive materials also contain nuclear energy.

Internal Energy is the energy stored in any object. It is the energy of the vibrating or moving atoms in the object.

Thermal/Heat Energy is energy travelling from a hotter (molecules have a higher average kinetic energy) to a cooler (molecules have a lower average kinetic energy) object.

Light Energy is a form of energy transferred through radiation.

Sound Energy is transferred in the form of vibration through the air.

Strain Energy is energy stored by an elastic object when deformed. This energy helps the object return to its original state.

Law of Conservation of Energy Energy can neither be created, nor destroyed. It can only be converted to different forms.

The total amount of energy before and after any conversion is constant, though some of this energy may have been wasted.

Energy Efficiency

The efficiency of an energy conversion is the fraction of the energy that results in the desired form.

Efficiency of an object (%) =

Work and Power

Work done (J) = Energy transferred (J) OR W = E

Work done (J) = Force (N) Distance moved in the direction of the force (m) OR W = F d

Power (W) = OR P = W/t

Energy Resources

Renewable (inexhaustible resources that can be replaced after use)

Hydropower: Potential energy of water stored at heights in dams is released, converting it into kinetic energy that turns a generator.

Geothermal Energy: The large thermal energy content inside the earths crust is harnessed by pumping water down to the rocks. Thermal energy is transferred from the rocks to the water, which boils. Kinetic energy present in high-pressure steam that results is used to turn a generator.

Solar Energy: In sunny countries, solar panels are used to absorb thermal energy directly from the sun. The thermal energy is used to heat water and form steam, whose kinetic energy turns a generator.

Wind Power: Kinetic energy of the wind is used to turn windmills that also function as turbines to turn a generator.

Wave/Tidal Power: The kinetic energy from wave movements is used to spin turbines connected to a generator.

Biomass Fuels: Chemical energy stored in organic matter is released by burning, generating thermal energy that fuels rural households. Can also be considered as non-renewable since some types of biofuels are exhaustible.

Non-renewable (exhaustible resources that cant be replaced after use)

Fossil Fuels: Chemical energy stored in hydrocarbons is released by burning. Their thermal energy is used to heat water to form steam, whose kinetic energy turns a generator.

Nuclear Power: The radioactive decay of some elements such as uranium is speeded up using the process of nuclear fission. This creates a chain reaction that releases large amounts of thermal energy from the atoms nuclear energy. Their thermal energy is used to heat water to form steam, whose kinetic energy turns a generator.

Advantages and Disadvantages

Energy Resource

Advantages

Disadvantages

Hydro-power

Renewable

Clean no carbon emissions

Depends largely on location

Building dams causes drastic environmental changes

High initial set-up costs

Wind power

Renewable

Clean no carbon emissions

Need a large area/scale

Irregular source

High maintenance costs

Wave power

Renewable

Clean no carbon emissions

Inefficient due to irregular wave patterns

Depends largely on location

High maintenance and very high installation costs

Solar power

Renewable

Clean no carbon emissions

Works only during the day and during certain types of weather

High initial costs

Requires a very large scale/area

Geothermal energy

Renewable

No carbon emissions

Can be used directly and easily

Relatively cheap usage

Not a widely available source

Suited only for particular regions

Can release harmful gases from deep in the earth

High initial costs

Biomass fuels

Renewable

Easily available

Carbon emissions pollute the air and contribute to global warming

High production costs

Fossil fuels

Relatively cheap

Can be used directly and easily

Non-renewable

Carbon emissions pollute the air and contribute to global warming

Nuclear power

Very high power output

No carbon emissions

Large reserves of nuclear fuels are present in the environment

Difficult and expensive to dispose of radioactive wastes produced

Could easily go out of control and cause a health hazard

Uranium mining tends to be difficult

Topic 5: Kinetic Model of Matter

State

Volume

Shape

Arrangement of particles

Movement of particles

Energy

Solid

Fixed volume

Fixed shape

Packed closely together in a regular arrangement

Vibrate about a fixed position

Vibrational

Liquid

Fixed volume

Takes the shape of its container

Slightly less closer than in a solid, but particles are still in contact with each other

Vibrate and slide over each other fluid

Vibrational and translational

Gas

Expands to fill its container

Takes the shape of its container

Widely separated from each other and do not come on contact with each other unless they collide

Move freely around, and colliding with each other & the containers walls fluid

Vibrational, translational and rotational

Movement of Particles

Brownian motion: the continuous random movement of a fluid particle

The straight path of a moving particle changes in direction when it collides with other particles or the walls of the container.

Change of State

Boiling or Evaporating

Melting

Solid Liquid Gas

Freezing

freezing

Condensing

All state changes (except evaporation) occur at fixed temperatures

Boiling point = Freezing point

Melting point = Condensation point

At the boiling and melting points, heat energy is not being used to raise the temperature of the substance, it is used to overcome the attractive forces between the particles to move them further apart

When solids are heated, they vibrate more strongly, expanding. When they vibrate with a sufficient strength, the bonds between them are broken, forming a liquid

Evaporation and Boiling

Evaporation

Boiling

Can occur at any temperature (normally below the boiling point)

Occurs at a fixed temperature (boiling point)

Only takes place at the surface of the liquid

Takes place throughout the liquid

No bubbles are produced

Bubbles are produced

Slower process

Relatively faster process

Temperature of the liquid decreases

Temperature of the liquid doesnt change

Factors affecting evaporation: -

1. Temperature: at a higher temperature more of the particles of the liquid are moving fast enough to escape from the surface

2. Surface area: with a greater surface area, more of the particles are close to the surface so they can escape more easily

3. Moving air/Draught: when particles escape from the water, they are blown away, thus maintaining a concentration gradient for more particles to evaporate.

Topic 6: Thermodynamics

Temperature (K) is a measure of the average kinetic energy of the individual particles of a substance.

Internal Energy (J) is the total energy of all the particles.

Thermal Equilibrium is when no net energy transfer occurs between multiple surfaces since their particles all contain the same average kinetic energy.

Measuring Temperature

1. Thermometers (liquid-in-glass) work on the principle of expansion of liquids with heat. The Celsius scale is calibrated by first placing the thermometer in melting ice then waiting for it to reach equilibrium to mark 0C. the same is done just above boiling water for 100C. Factors necessary to form such a thermometer:

Sensitivity is a property wherein a small change in temperature causes a large change in the liquid column

Linearity is a property wherein the expansion/change in length displayed by the liquid is proportional to its temperature

2. Thermocouples are devices that give an output voltage that is proportional to the temperature. They are made from two pieces of wire made of two different metals (normally copper and iron). The wires are joined to form two junctions. One junction is kept at a fixed temperature of 0C (calibrated by placing in melting ice) while the other is placed in the object whose temperature is to be measured. The difference in temperature is reflected as the potential difference in voltage between the junctions.

Thermal Expansion most substances (solids, liquids and gases) expand on heating as the particles begin to move faster and away from each other.

Heat Capacity

Heat Capacity of a body is the amount of thermal energy required to raise its temperature by 1C or 1K.

Thermal Energy required (J) = Heat capacity (J/K or J/C) Change in temperature (K or C) OR Q = CT

Specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1kg of the substance by 1C or 1K.

Thermal Energy required (J) = Mass (kg) Specific heat capacity (J/kgK or J/kgC) Change in temperature (K or C) OR Q = mcT

Latent Heat

Latent Heat of a body is the amount of thermal energy absorbed or released during a change of state.

The specific latent heat of vaporization is the energy required to cause 1kg of a substance to change its state from liquid to gas at its boiling point.

The specific latent heat of fusion is the energy required to cause 1kg of a substance to change its state from solid to liquid at its melting point.

Thermal Energy required (J) = Latent heat (J/kg) Mass (kg) OR Q = mL

Heat Transfer

Thermal/Heat energy is only transferred when there is a difference in temperature

Heat is transferred from a region of higher temperature to a region of lower temperature until the regions reach thermal equilibrium

Heat Transfer Methods:

1. Conduction is the process by which heat is transmitted through a medium from its hotter part to its colder part until they are both at the same temperature

When a part of an object (medium) is supplied with thermal energy, the particles at that part gain kinetic energy. They vibrate faster and collide with the neighboring particles.

As the particles collide, kinetic energy is transferred. The less energetic particles gain kinetic energy, vibrate faster, and collide with other less energetic particles in the colder part of the object.

This continues until the heat energy spreads throughout the object.

Tends to happen more in solids since the particles are closer together.

Metals are good heat conductors since they contain free electrons, which are not possessed by non-metals. E.g. Copper, Steel, Aluminum

Non-metals are poor heat conductors (insulators). E.g. Plastic, Wood, Air

2. Convection is the process by which heat is transmitted from one place to another by the movement of heated particles in a fluid

When thermal energy is supplied to a region of the fluid, it expands.

This region becomes less dense than the surrounding fluid and thus rises.

The other cooler, denser regions of the fluid sink to replace the less dense fluid.

This creates convection currents the flowing of a liquid or gas caused by a change in density in which the entire medium moves and carries the heat energy with it.

3. Radiation is a method in which heat energy is transferred from a hotter to a cooler object in the form of electromagnetic waves, specifically infrared radiation

Objects tend to absorb as well as emit infrared radiation

This process can take place in a vacuum; it does not require a medium.

When emitted radiation reaches an object, heat energy is absorbed, making its molecules vibrate faster.

Different objects emit and absorb different amounts of radiation at different rates.

Good absorbers of heat are also good emitters.

Other objects that do not absorb heat are termed as reflectors.

Faster radiation

Slower radiation

Color and texture

Dull black surfaces (emitters/absorbers)

Bright and shiny surfaces (reflectors)

Surface area

Larger

Smaller

Temperature difference

Higher

Lower

Factors affecting radiation

Topic 7: Waves and Sound

A wave transfers energy through disturbances in its environment no matter is transferred in the process.

Types of Waves

A)

Electromagnetic

Mechanical

Do not need a medium

Form a full spectrum

An electric field oscillates perpendicular to the wave motion

Need a medium

Example sound, springs, water waves

B)

Transverse

Longitudinal

Direction of motion of the oscillating particles is perpendicular to the direction of motion of the wave/energy transfer/disturbance

Upwards/downwards oscillation

Can occur in both mechanical and electromagnetic waves

Distance/displacement variation based on that of the mean position

Example ripples, all electromagnetic waves

Direction of motion of the oscillating particles is parallel to the direction of motion of the wave/energy transfer/disturbance

Forward/backward (sideways) oscillation

Only occurs in mechanical waves

Pressure variations based on that of the mean position

Sound

Important terms in describing waves

1. Mean position: the center where the disturbance originates an undisturbed point (also called an equilibrium point). Every particle has a mean position that it oscillates about.

2. Displacement: shortest distance of the oscillating particle from the mean position measured at a certain point in time.

3. Time period: time taken to complete one oscillation (s).

4. Amplitude: maximum displacement of a particle from its mean position. Amplitude energy level of the wave.

5. Crest: the position of maximum positive displacement of a wave.

6. Trough: the position of maximum negative displacement of a wave.

7. Compression: a region of a longitudinal wave wherein the particles of the medium move closer together thus creating maximum pressure and displacement from the mean position (also maximum density). The distance of the center of compression from the mean position is the crest.

8. Rarefaction: a region of a longitudinal wave wherein the particles of the medium move further apart thus creating minimum pressure and displacement from the mean position (also minimum density). The distance of the center of rarefaction from the mean position is the trough.

9. Wavelength: the distance traveled by the wave during one time period. The distance between two successive crests/troughs. Wavelength varies with density of the medium.

10. Frequency: number of complete waves/oscillations per second does not change with density of the medium.

11. Speed of the wave: proportional to wavelength.

12. Wavefront: a line joining successive crests/troughs/same points on a wave.

Frequency (Hz) = OR f =

Speed of the wave (m/s) = Wavelength (m) Frequency (Hz) OR V = f

Wave effects

1. Reflection: the wave is reflected from a vertical surface at the same angle as it strikes it

2. Refraction: occurs when the density of a medium changes thus changing the speed of the wave and making it change direction frequency remains constantComment by Diva Parekh: Doesnt a waves speed increase in solids? Because sound is faster in concrete than liquids requires further explanation (only longitudinal waves travel faster in solids)

3. Diffraction: the waves bend around the sides of an obstacle or spread out while passing through a gap (gaps wider than the wavelength produce less diffraction)Comment by Diva Parekh: Verify why in terms of a wave diagram question 4 on page 129

Sound

Sound waves are mechanical and longitudinal waves caused by vibration in a medium (can be solid, liquid or gas sound cannot travel through a vacuum)

Speed of sound:

In dry air at 0C = 330 m/s

In dry air at 30C = 350 m/s

Pure water at 0C = 1400 m/s

Concrete = 5000m/s

Refraction of sound = Since sound travels slower at cooler temperatures closer to the ground and faster at higher temperatures (occurs at night), waves bend towards the ground as a result of the change in speed

Reflection of sound = Hard surfaces reflect sound waves in the form of echoes.

Speed of sound =

***Used to measure distances and depths since speed is already known

Frequency Pitch of sound = Humans can detect sounds from a frequency of 20 Hz to 20,000 Hz. Sounds higher than this range are called ultrasonic.

Amplitude Loudness of sound (decibels)

Quality of sound = when sounds have the same fundamental frequency mixed in with different weaker frequencies called overtones, they have differing qualities.

Light

A form of radiation (spreads out from its source) that travels in straight lines

Travels as an electromagnetic wave; can travel through a vacuum

Speed of light in a vacuum = 3 108 m/s

Properties: -

1. Reflection

Only occurs when the light ray cannot pass through the surface

Ray striking the surface = incident ray

Ray leaving the surface = reflected ray

Line perpendicular to the surface = normal

Angle that the incident ray makes with the normal = angle of incidence

Angle that the reflected ray makes with the normal = angle of reflection

Angle of incidence = angle of reflection

Regular reflection

Diffused reflection

Reflection of rays on a smooth plane surface all incident rays have parallel reflected rays

Reflection on an irregular surface rays are reflected in different directions

Forms an image on the surface

Doesnt form an image

Image formed in a plane mirror:

The same size as the object

Upright and laterally inverted

Virtual

As far behind the mirror as the object is in front

A line joining equivalent points on the object and the image passes through the mirror at right angles

2. Refraction

Refers to the bending of light when it passes through a medium of different density due to the change in its speed

Angle of refraction = the angle that the refracted ray makes with the normal

Snells Law:

When light is refracted from a rarer to a denser medium, an increase in the angle of incidence (i) produces an increase in the angle of refraction (r): = constant = refractive index

Refractive index is also =

Situations of refraction:

a. When light travels from a rarer to a denser medium

Ray is refracted towards the normal

Speed decreases

Angle of incidence > angle of refraction

Total internal reflection can occur: -

Critical angle = the angle of incidence in the denser medium for which its angle of refraction into the rarer medium is 90 =

Total internal reflection is when light travels from a denser medium to a rarer medium and the angle of incidence is greater than the critical angle, there is no refracted ray since all the light is reflected back into the denser medium

b. When light travels from a denser to a rarer medium

Light is refracted away from the normal

Speed increases

Angle of incidence < angle of refraction

c. When light enters a medium perpendicular to its surface

Light ray does not bend

Speed changes according to the difference in density of the medium

Angle of incidence = angle of refraction = 90

Lenses

a) Concave lenses: thicker around the edges than at the center light rays are diverged (bent outwards)

b) Convex lenses: thicker at the center than at the edges light rays are converged to a single point after passing through

Drawing ray diagrams

The point where the rays converge is called the principal focus

The distance of the principal focus from the center of the lens is called the focal length

The line joining the principal focus to the center is the principal axis

A ray needs to be drawn joining a point on the object through the center of the lens

Another ray from the object running parallel to the principal axis passes through the focus after leaving the lens

The intersection of these two rays forms a point on the image

If an object is closer to the lens than the focus, it will form a virtual, upright image (normally magnified) because it cannot be formed on a screen (no rays meet to form it)

If an object is further from the lens than the focus, it will form a real, inverted image (normally diminished) because it can be formed on a screen (rays meet to form it)

Linear magnification =

Correcting defects in vision

a) Short sight: the lens cannot be made thin enough to look at distant objects. As a result of excessive bending of light the rays converge before reaching the retina. Concave lenses are used to correct this.

b) Long sight: the lens cannot be made thick enough to look at close objects. As a result of insufficient bending of light the rays do not meet by the time they reach the retina. Convex lenses are used to correct this.

Topic 8: Electricity

Static Electricity

There are two types of electric charges; positive and negative

Like charges repel, unlike charges attract

The closer the charges are, the greater the electric forces acting between them

Electric field lines denote the path taken by a test positive charge since they denote the net effective charge, electric field lines can never intersect

Charge of one electron = 1.6 10-19 C

Charge of one proton = 1.6 10-19 C

Electric field lines: -

Isolated charges Charged plates

Static electric charges

An object becomes negatively charged when it gains electrons and positively charged when in loses electrons

Static charges can be acquired through friction or earthing

Electrostatic induction occurs when a conductor becomes charged when a charged body is brought near but not in direct contact with it

Conductors and insulators:

a) Conductors allow electrons to pass through them. Metals are good electrical conductors due to the presence of free, mobile electrons they lose charge almost immediately.

b) Insulators contain tightly bound electrons that are not free to move. Non-metals and plastics are good insulators they can accumulate charge without losing it to the surroundings.

c) Semiconductors are poor conductors when cold but good conductors when warm. Examples are silicon and germanium.

Electrical Circuits

Quantity

Abbreviation

Unit

Definition

Current

I

Ampere (A)

The amount of charge flowing through a circuit per unit time (travels from positive to negative)

Charge

Q

Coulomb (C)

The quantity of unbalanced positive or negative electricity in a body

Time

t

Seconds (s)

-

Voltage

V

Volts (V)

An electromotive force (the energy required to push one unit of charge through a circuit) or the potential difference (work done in moving one unit charge through the circuit component).

Energy

E

Joules (J)

-

Power

P

J/s or Watts (W)

Rate at which a substance transforms energy

Resistance

R

Ohms ()

The degree to which a material opposes the passage of an electric current

Formulae

1.

2. V = IR (Ohms Law)

3. E = QV = I t V

4. Q = I t

5. W = IV

6. R = where rho or is the specific resistivity constant (given that the temperature is constant) that varies with the material used

= (for the same material)

7. P = VI

8. P = I2R

9.

Series and parallel circuits

Series circuits

Parallel circuits

If one component is removed or disconnected, all the others stop working because the circuit is broken

If one component is removed, the others still function because they are connected by an unbroken circuit

Each component shares the voltage from the battery

Each component gets the full voltage from the battery because each is connected directly to it

Total voltage = sum of the potential difference across each component

Voltage through each component is the same

The current through each component is the same

Total current = sum of the currents in the branches

Overall circuit resistance increases with the number of resistors

Total resistance = sum of resistance across each individual resistor

R = R1 + R2 +

If two or more resistors are connected in parallel they give a lower resistance than that of any individual resistor

(for two resistors)

Symbols used to depict Electrical Circuit Components

Component

CircuitSymbol

Cell

Battery

Direct Current supply

Alternating Current supply

Fuse

Earth (Ground)

Lamp(indicator)

Inductor (Coil, Solenoid)

Switch

Resistor

VariableResistor (Rheostat)

Voltmeter

Ammeter

Connecting wire

c)

Topic 8: Magnetism

Properties of magnets:

A magnet has a north pole and a south pole

Law of magnetic poles = like poles repel, unlike poles attract (repulsion occurs only when both poles are magnets)

The magnetic field is strongest at the two poles

Only magnetic materials (iron, nickel, cobalt) are attracted by magnets

Magnetic field lines

Bar Magnet Repulsion Attraction

Induced magnetism:

A permanent magnet can temporarily pass its magnetism to a magnetic material

When a magnetic material is placed near to or in contact with a permanent magnet, its poles align themselves, inducing magnetism in it

Soft magnetic materials are magnetized faster, but retain magnetic properties for less time E.g. Iron

Hard magnetic materials take longer to be magnetized, but retain their magnetism for longer E.g. Steel

Methods of magnetization:

Magnetization by stroking the magnetic material can be stroked several times by the poles of permanent magnets. Using two magnets (double/divided touch) is faster than using one (single touch).

Electrical method placing the material inside a solenoid and connecting it to a direct current thus exposing it to the strong magnetic field created by an electromagnet.

Methods of demagnetization:

Heating and hammering this causes the magnetic poles alignment to become irregular again.

Electrical method placing the magnet inside a solenoid and connecting it to an alternating current.

General: Important Points and common mistakes

During circular motion, even though the speed does not change, there is a constant change in direction therefore change in velocity. This mean that the object is CONSTANTLY ACCELERATING there is a centripetal acceleration towards the center of the force

In a velocity/time graph, if an object travels up and then back down in a straight line (e.g. a ball thrown upwards) one direction will be shown as positive while the other will be shown as negative [the line will extend below the x-axis]

While parachuting, at first the person is free falling towards the ground at a constant acceleration (10 m/s2). The air resistance balances the acceleration and the object reaches terminal velocity. When the parachute is opened, air resistance increases greatly, slowing the person down. The gravity then balances the increased air resistance and the person reaches a slower terminal velocity. There is no further acceleration until the person reaches the ground.

When any question on force is asked, dont forget to mention direction since force is a vector and is meaningless without direction.

ALWAYS MENTION UNITS UNLESS THE QUESTION HAS WRITTEN UNITS IN THE BLANK

ALWAYS LABEL DIAGRAMS AND USE ARROWS FOR FORCES

WHEN SHOWING WEIGHT, ALWAYS DRAW THE LINE FROM THE CENTRE OF MASS

DURING ANY MEASUREMENT QUESTIONS READ THE SCALE

When a fairly ELASTIC object is dropped at the beginning, it will have zero speed, and then it accelerates constantly towards the ground (free fall). Air resistance slows it down until it reaches a terminal velocity. The object maintains the same speed until it hits the ground. It DOES NOT LOSE ITS ENERGY WHEN IT TOUCHES THE GROUND AT FIRST. The energy still remaining causes it to be compressed, after which its speed becomes zero, and then it rebounds with a lower maximum height than previously.

In measurement diagrams, ALWAYS ALIGN THE ZERO MARK WITH THE EYE LEVEL.

When asked for the OVERALL change in velocity, it is always FINAL INITIAL

Latent heat of FUSION is ALWAYS LESS than that of VAPORIZATION

Gravitational potential energy is always calculated using the VERTICAL DISTANCE moved by the object

When calibrating a thermometer, it should be either placed JUST ABOVE boiling water or inside PURE boiling water. Not in boiling water since the waters purity here is not specified.

Impurities increase boiling point and decrease melting point some impure substances can also boil over a range of temperatures

Gases have the most potential energy and solids have very little. Specific heat capacity in gases is higher due to this.

When changing in state, there is NO CHANGE IN KINETIC ENERGY, only INTERMOLECULAR SPACING CHANGES.

When the question asks to define - pay attention to whether it is SPECIFIC heat capacity or just HEAT CAPACITY and define accordingly

When drawing Brownian motion MAKE ARROWS

Pay attention to the axis titles in distance/time/speed graphs