Electricity Worksheet18

How will you join three resistances, each of 2 Ω so that the effective resistance is 3 Ω?

On what factors does the resistivity of a material depend ?

What happens to the current in a circuit if its resistance is doubled ?

What happens to the resistance of a circuit if the current through it is doubled ?

What happens if the potential difference across a resistance is doubled ?

How does the resistance of a wire depend upon its radius ?

How does the resistance of a wire depend on its length?

How does the resistance of a metallic wire depend on its temperature.

Two wires are of the same length, same radius, but one of them is of copper and the other is of iron. Which will have more resistance ?

Find the pd required to pass a current of 0.2 A in a wire of resistance 20 Ω.
Answer:

A parallel combination of two resistances (which will be 1 Ω) joined in series with the third resistance (2 Ω).

It depends only on the nature of the material.

The current is reduced to half its previous value.

The resistance of the circuit does not depend on the current through it.

The current through the resistance is doubled as I = V/R.

The resistance of wire, R ∝ 1/r^{2} where r is the radius of the wire.
(R = Pl/A, i.e., R ∝ 1/A or R ∝ I/ πr^{2} R ∝ I/r^{2})

The resistance of a wire, R ∝ I where l is the length of the wire.

The resistance of a metallic wire increases with temperature.

As R = pl/A and p for iron is more than that for copper, so the iron wire has more resistance.

Ohm's law, V = IR = 0.2 × 20 = 4V.