Question

Answer the following:

(1) P and Q are the two wires of same length and different cross sectional areas and made of same metal. Name the property which is same for both the wires and that which is different for both the wires.

(2) Resistivity of some material is given below. State which one will be the best conductor.

Material		Copper		Aluminium		Silver		Nickel
Resistivity (Ωm)		1.62 × 10−8		2.63 × 10−8		1.60 × 10−8		6.84 × 10−8

(3) If the resistance of wire A is four times the resistance of wire B, find the ratio of their cross sectional areas.

(4) Two dissimilar bulbs are connected in series, which bulb will be brighter?

Answer 1

(1) Since both the wires P and Q are made of same material, resistivity (a characteristic property of a material, independent of the dimensions of the material) for both must be same while due to different cross section area they have different resistance (depends upon the dimension of the material).

(2) Resistivity is the measure of a material’s ability to oppose the flow of current. Thus less the resistivity that means more the conductivity and better be the conductor.

From the given data, silver is the best conductor among all.

(3) Given:

R_A = 4 R_B ---------- (1)

A_A : A_B = ?

Let us assume that length and the resistivity of the wire A are l_A & ρ_A respectively and that of wire B are l_B & ρ_B .

Now as,

(4) We can consider the bulbs in terms of their resistance.

The power of a bulb determines its brightness and is written as:

P = I²R

So, Power is proportional to the resistance.

The bulb with more resistance will have more power and will thus be brighter.