Question

QUESTION - A small bulb has a resistance of 2Ω when cold. It takes up a current of 0.4 A from a source of 4V and then starts glowing. Calculate (i) the resistance of the bulb when it is glowing and (ii) Elaborate on the reason for the difference in resistance?

Answer 1

Given,

Resistance (R cold) = 2 Ohm

Current (I) = 0.4 Ampere

Voltage (V) = 4V

Let us calculate the resistance when it is glowing by using Ohm’s law.

According to Ohm’s law,

V = I x R

R=VI

Substituting the values in the above equation, we get

R = 4/0.4

R = 10 Ohm

Answer 2

Given that -

• A small bulb has a resistance of 2Ω when cold.
• It takes up a current of 0.4 A from a source of 4V and then starts glowing.

To calculate -

• 1) The resistance of the bulb when it is glowing.
• 2) Eaborate on the reason for the difference in resistance.

Full solution -

1) Answer is followed -:

As it's already given that,

• Resistance = 2 Omega
• Current = 0.4 Ampere
• Voltage = 4V

Using concept are given below,

• Resistance = V/I

Where, the following denotes

• V denotes voltage.
• I dentoes Current

Putting the values we get the results,

• Resistance = V/I
• Resistance = 4/0.4
• Resistance = 10 Ω

2) Answer is followed -:

• As it's already given that a small bulb has a resistance of 2Ω when cold then it takes up a current of 0.4 A from a source of 4V and then starts glowing. Means, the resistance of conductor changes with change in temperature of given conductor.

• When the temperature of a conductor increased the energy of atoms inside the conductor also increase, which causes molecules & atoms of conductor to collided on each other.

• In short when the resistance increase with an increase in the temperature.