Current Electricity – Test Paper
Class 12 Physics (chapter 3)
Time: 1 Hour
Max Marks: 35
Section A –MCQs [1 × 5 = 5 marks]
1. 1. The current in a wire of non-uniform cross-section:
a) Is different at different points
b) Depends on the potential
c) Is the same at all points
d) Becomes zero in thinner regions
2. 2. When temperature increases, the drift velocity of electrons in a conductor:
a) Increases
b) Decreases
c) Remains constant
d) First increases, then decreases
3. 3. The resistivity of a material depends on:
a) Length and area
b) Only temperature
c) Material and temperature
d) Material and dimensions
4. 4. Which of the following combinations gives minimum resistance?
a) Three 6 Ω resistors in series
b) Three 6 Ω resistors in parallel
c) Two 6 Ω in series, one in parallel
d) All in mixed combination
5. 5. If current I is flowing in a conductor of resistance R, then power dissipated is:
a) IR
b) I²R
c) IR²
d) I/R
Section B – Short Answer Questions [2 × 5 = 10 marks]
6. A wire is stretched to 3 times its original length without changing its volume. Will
resistivity change? Justify logically.
7.Even though drift velocity is very small (~mm/s), electric bulbs light up instantly
when switched on. Why?
8. Explain why alloys like nichrome are used in heating elements instead of pure metals
like copper.
9. Write an expression for relaxation time and explain its role in determining resistivity.
10. Explain with reason: Resistance of a conductor increases with temperature, but that of a
semiconductor decreases
Section C – Numerical Questions [5 x 4 = 20 marks]
11. Assume a hypothetical wire where positive charges (protons) move instead of electrons.
If the drift velocity of protons is equal in magnitude to that of electrons in a normal
conductor,
(a) What will be the opposite direction of the direction of current in this case?
(b) Will resistance and power loss formulas remain the same?
12.A wire is infinitely long and made of a material with zero resistivity (ρ = 0). It is
connected to a 12 V battery at one end, with the other end left open.
(a) What is the potential difference between two points 1 m apart on the wire?
(b) Will current flow? If yes, how much?
(c) What is the electric field inside the wire?
13.Three resistors R1 = 6 ohm, R2 = x ohm, and R3 = 3 ohm are connected in the
following way:
R1 and R2 are connected in parallel.
This parallel combination is connected in series with R3.
The total equivalent resistance of the circuit is 5 ohm.
(a) Find the value of x.
(b) If a 20 V battery is connected across the entire combination, calculate the total current
drawn from the battery.
(c) Calculate the power dissipated in resistor R2.
14.A metal wire of resistance 3Ω is elongated to make a uniform wire of double its previous
length. This new wire is now bent and the ends joined to make a circle. If two points on
this circle make an angle 60 degree.
At the center, the equivalent resistance between these two points will be
