what exactly does each part of the circuit do?

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor

What exactly does each part of the circuit do?

Measures current Circuit control Source of Electrical

Supply Circuit protection Measures electrical

pressure Circuit load Conductor

Open Circuit

Closed Circuit

Short Circuit

What is:

How to decode a resistor.

All components of an electrical circuit have resistance (including the conductors).

A resistor is a component that is specifically designed to oppose current flow.

Resistors are generally made from alloys of metal or carbon based compounds

A few are made from semi-conductor type material (like silicon)

What is a resistor?

Linear resistors – wire wound

Linear resistors – carbon compound

The power rating of a resistor is the amount of heat (I2R – in watts) that a resistor can dissipate before the losses are too great or the resistor is destroyed.

For large power ratings resistance wire is used whereas for low (and physically small) power ratings carbon based resistors are used.

Power ratings of res

To make manufacturing cheaper a series of standard values are manufactured.

These vary for the three main tolerance ranges. Tolerance is the degree of accuracy that the

resistor had been manufactured to. For example a 10Ω resistor with a silver

tolerance band has a tolerance of ±10% and can range from 9Ω to 11Ω.

A variable or “tuning” resistor can be placed in a circuit to compensate for the difference.

Tolerance and preferred values of resistance

Temperature sensitive resistors 2 types

Positive temperature coefficient (PTC)

Negative temperature coefficient (NTC)

PTC – resistance increases with an increase of temperature. Made from metallic oxide or silicon.

NTC – resistance decreases with a decrease of temperature. Made from chromium or nickel with small amounts of semi-conductor material.

Non-linear resistors - Thermistors

Resistance varies as the voltage varies

Used for lightning protection where under normal circumstances the do not conduct but when the voltage reaches a certain level the resistance drops.

Uses also include over voltage protection and signal compensation.

Non-linear resistors – Voltage dependant resistors (VDRs)

Resistance varies as the light varies Usually made from cadmium sulphide

mounted on a plate and covered with a vacuum-deposited metallic grid

Non-linear resistors – Light dependant resistors (LDRs)

Resistor (general) Variable resistor

(rheostat) Variable resistor

(potentionometer) Adjustable resistor PTC thermistor NTC thermistor Voltage dependant

resistor Light dependant resistor

Resistor circuit symbols

+ to C

- to C

Black Beer Rots Our Young Guts But Vodka Goes Well

Black is NO color - nothing, zeroBrown, think brow-ONE. Red, think TWO red lips.Orange, think "orange tree" tree rhymes with three.Yellow, think Yell FOUR help.Green, think of a green FIVE dollar billBlue, think "sick (six) and blue"Violet, think "violet clouds in heaven, rhymes with SEVEN.Grey, thing Gray-EIGHT (great)White, think of white wine, rhymes with NINE

Remembering the resistor colour code

Longer conductor =

How does length affect resistance?

Longer conductor = more resistance Shorter conductor =

How does length affect resistance?

Longer conductor = more resistance Shorter conductor = less resistance

How does length affect resistance?

Longer conductor = more resistance Shorter conductor = less resistance

Resistance α Length

How does length affect resistance?

Conductor cross sectional area

Larger conductor =

How does c.s.a. affect resistance?

Larger conductor = less resistance Smaller conductor =

How does c.s.a. affect resistance?

Larger conductor = less resistance Smaller conductor = more resistance

How does c.s.a. affect resistance?

Larger conductor = less resistance Smaller conductor = more resistance

Resistance α 1 c.s.a

How does c.s.a. affect resistance?

The measure of how resistive a material is, is called resistivity.

How does the conductor material affect resistance?

1 m 1 m

1 m

Ω

R = ρ x ℓ A

Where: R = resistance of conductor in ohmsρ = resistivity of conductors in ohm metersℓ = length of conductor in metersA = c.s.a. of conductor in meters2

Sooo…If we put all of them together…..

When current flows through a conductor it heats up

The amount of change in resistance is known as the temperature coefficient of resistance

If the resistance goes up – positive temperature coefficient (conductors)

If the resistance goes down – negative temperature coefficient (insulators and semiconductors)

How does temperature affect resistance?

Rh = Rc [1 + (α x Δt)]Where: Rh = Final (hot) resistance in ohmsRc = Initial (cold) resistance in ohmsα = Temperature coefficient of resistance in

omhs per ohms per degrees celciusΔt = difference in temperature in degrees

celcius

Equation for resistance and temperature

Most electrical components are made with a certain amount of smoke and if they get too hot it all gets let out!

Heat increases the resistance in conductors thereby increasing the voltage drop across the cable, also there is a risk of insulation meltdown – resulting in short circuit

Effects of temperature on a circuit

Motors, transformers, alternators and lamp filaments all start up with a lower resistance – leading to high starting currents.

R1 = ℓ1 hence R2 = R1 ℓ2

R2 ℓ2 ℓ1

But wait…..There’s more!

R1 = A2 hence R2 = R1 A1

R2 A1 A2

R1 = d22 hence R2 = R1 d1 2

R2 d12 d2

R2 = R1A1ℓ2

A2ℓ1

Series circuits