resistance and factors affecting it! episode 3

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Resistance and factors affecting It!Episode 3

ELE

CTR

ICIT

Y Electric Current & Potential Difference

Resistance & Factors Affecting it

Ohm’s Law

Heating effects of Electric Current

Resistance in Series

Resistance in Parallel

Electrical Power & Energy

V = IRV = I/R

V = W/Q I = R/V

A B

C D

Q1. Which formula represents Ohm’s law?

200 V 100 V

250 V 50 A

A B

C D

Q2. Calculate the potential difference between two points of a terminal, if an electric current of 10 A is flowing through it having resistance of 20Ω.

200 V 100 V

250 V 50 A

A B

C D


All appliances don’t follow ohm’s law

It depends on physical factors of the conductor like temperature, pressure

Both A and B

A

B

C

Q3. Why ohm’s law is not a universal law?

Q18. What is the potential difference between the ends of a conductor of 16 ohm resistance, when a current of 1.5 A flows through it?

ANSWER : 24 V

Remember Resistance?

How is resistance caused?

Electrons Atoms

Impurities All of these

A B

C D

Q4. What kind of particles is present inside a conductor?

Electrons Atoms

Impurities All of these

A B

C D


Electrons Protons

Impurities Neutrons

A B

C D

Q5. Which one of the particles moves when potential difference is applied across it?

Electrons Protons

Impurities Neutrons

A B

C D


Liar ! Chal Jhute!! Yes! Hoga Sir!

A B

Q6. Do you think electrons have eyes?

These electrons collide with atoms.

These collision causes them to lose momentum and slow down.

These electrons collide with atoms.

It’s like walking through a crowded road!

No matter how fast you want to go you can’t gain speed.

You keep losing momentum.

It’s like walking through a crowded road!

These collisions are the opposition to the flow of electrons.

These collisions are the opposition to the flow of electrons.

This collision is called Resistance.

More Collision more will be the resistance.

Less Collision less will be the resistance.

For an electron to travel a distance of 15 cm it takes 2 mins.

For an electron to travel a distance of 15 cm it takes 2 mins.

Then how is electricity so fast?

220 V25 V

11 V 110 V

A B

C D

Q7. With What voltage you get electricity at home?

No Yes

A B

Q8. Is it possible to change that voltage?

NoYes

A B

Q9. Does the devices like Tubelight, refrigerator and mobile phone take the same current?

How can we reduce the current?

We know, Resistance in a conductor is the result of collision in it.

Let’s see what are the factors that affect the number of collisions

Consider 2 Hose Pipes

Less Resistance

More Resistance

As length increases collision increases and resistance increases

As length increases collision increases and resistance increases R ∝ l

Less Resistance

More Resistance

As cross section increases , space for electron increases, collision decreases, so resistance decreases

As cross section increases , space for electron increases, collision decreases, so resistance decreases R ∝ 1/A

Combining both,

Combining both,

We insert a constant,

The constant is resistivity.

Combining both,

We insert a constant,

Resistivity is the resistance offered by a conductor of unit cross section and unit length.

What really is resistivity?

Ohm/ metre Ohm metre

A B

Q10. What is the SI unit of Resistivity?

Ohm/ metre2 Ohm metre2

C D

No Yes

A B

Q11. Will temperature Affect resistance?

As temperature increases collision increases, Resistance increases.

Factors A ecting Resistance are:

1. Length of the Conductor2. Cross Sectional area of the

conductor3. Resistivity of the conductor4. Temperature of the material

Q12. The figure shows three cylindrical copper conductors along with their face areas and lengths.Discuss in which Geometrical shape the resistance will be the highest. [2013-Boards]

1.25 Ω 5.47 Ω

3.5 Ω 0.5 Ω

A B

C D

Q13. Calculate the resistance of 1 Km long copper wire of radius 1 mm. Resistivity of copper is 1.72 x 10-8 ohm m. [2013-Boards]

Q13. Calculate the resistance of 1 Km long copper wire of radius 1 mm. Resistivity of copper is 1.72 x 10-8 ohm m. [2013-Boards]

1.25 Ω 5.47 Ω

3.5 Ω 0.5 Ω

A B

C D

Q13. Calculate the resistance of 1 Km long copper wire of radius 1 mm. Resistivity of copper is 1.72 x 10-8 ohm m

6 x 10-6 Ω m 4 x 10-6 Ω m

6.86 x 10-8 Ω m 7.06 x 10-8 Ω m

A B

C D

Q14. Resistance of a metal wire of length 5 m is 100 ohm . If the area of cross-section of the wire is 3 x 10–7 m2, calculate the resistivity of the metal. [2019 Boards]

6 x 10-6 Ω m 4 x 10-6 Ω m

6.86 x 10-8 Ω m 7.06 x 10-8 Ω m

A B

C D


Doubled Halved

Four times One fourth

A B

C D

Q15. The area of cross section of wire becomes half when its length is stretched to double.The new resistance of wire becomes

Doubled Halved

Four times One fourth

A B

C D


Q16. The area of cross section of wire becomes half with change in volume. The new resistance of wire becomes

Q17. V I graph of two wires A and B are shown in the figure.If both wires are of same length and same thickness, which of the two is made of material of high resistivity. [2014-Boards]

Q18. Length of a copper wire is 1 m and its cross sectional area is, 0.001 m2. Calculate the resistance of the wire if resistivity of copper is 1.62 x 10-8 ohm m.

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resistance and factors affecting it! episode 3

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