Question bank Class 12 Physics Chapter 9. CURRENT ELECTRICITY
Standard:- 12th
Question Bank
Subject:- Physics
Chapter 9. CURRENT ELECTRICITY
MCQ’S (1 Mark Each)
1) Kirchhoff’s second law (voltage law) is based on
a) conservation of charge
b) conservation of mass
c) conservation of energy
d) conservation of momentum
Ans: c) conservation of energy
2) When unknown resistance is determined by meter bridge, the error due to contact resistance
is minimised by
a) connecting both the resistances only in one gap
b) interchanging the position of known and unknown resistances
c) using uniform wire
d) obtaining the null point near the ends of the wire
Ans: b) interchanging the position of known and unknown resistances.
3) The SI unit of potential gradient is
a) V/cm b) V-m
c) V/m d) V-cm
Ans: c) V/m
4) Instrument which can measure terminal potential difference as well as electromotive force
(emf) is
a) Wheatstone’s meter bridge
b) voltmeter
c) potentiometer
d) galvanometer
Ans: c) potentiometer
5) When null point is obtained in the potentiometer, the current is drawn from the
a) main battery
b) cell battery
c) both main and cell battery
d) neither main nor cell battery
Ans: a) main battery
6) If potential gradient of a wire decreases, then its length
a) remains constant
b) decreases
c) increases
d) none of the above
Ans: c) increases
7) Four resistances 4 Ω,8Ω, XΩ and 12Ω are connected in a series to form Wheatstone’s network. If the network is balanced, the value of X is
a) 24 b) 18
c) 12 d) 8
Ans: a) 24
Very Short Answer (VSA) ( 1 MARK Each )
1) State Kirchhoff’s first (current) law.
2) State Kirchhoff’s second (voltage) law.
3) What is the basis of Kirchhoff’s current law and voltage law?
4) Are Kirchhoff’s laws applicable to both AC and DC circuits?
5) Define potential gradient.
6) On what factors does the potential gradient of the wire depend?
7) What is the SI unit of potential gradient?
8) State any one use of a potentiometer.
9) A voltmeter has resistance of 100 Ω. What will be its reading when it is connected across a cell of emf 6 V and internal resistance 20 Ω? (Ans: 5 V)
10) In a meter bridge, two unknown resistances R and S, when connected between the two gaps, gives a null point is 60 cm from one end. What is the ratio of R and S?
(Ans: 3/2 )
Short Answer I (SA1) ( 2 MARKS Each )
1. What are the disadvantages of a potentiometer over a voltmeter?
2. Distinguish between a potentiometer and a voltmeter.
3. Distinguish between an ammeter and a voltmeter.
4. How do you calculate the shunt required to increase the length small n times?
5. Define: a) electrical circuit b) Junction
6. Calculate the value of the shunt resistance when connected across a galvanometer of resistance 18Ω will allow 1/10 th of the current to pass through the galvanometer.
(Ans: S = 2Ω)
7. Four resistances 6Ω,6Ω,6Ω and 18Ω form a Wheatstone bridge. Find the resistance which connected across the 18Ω resistance will balance the network. (Ans: 9 Ω)
8. The maximum safe voltage that can be measured using a galvanometer of resistance G is Vm . Find the resistance to be connected in series with the galvanometer so that it becomes a voltmeter of range nVm. [ Ans: (n-1) G ]
Short Answer II (SA2) ( 3 MARKS Each )
1) Explain with a neat circuit diagram. How you will determine the unknown resistances
using a meter bridge.
2) State any two sources of errors in the metre bridge experiment. Explain how they
can be minimised.
3) What is potential gradient? How is it measured? Explain.
4) Describe how a potentiometer is used to compare the emf’s of two cells by connecting
the cells individually.
5) A cell of e.m.f 1.5V and negligible internal resistance is connected in series with a
potential meter of length 10 m and total resistance 20 Ω. What resistance should be
introduced in the resistance box such that the potential drop across the potentiometer
is one microvolt per cm of the wire? 3 ( Ans : 29980 Ω )
6) In a meter bridge, the balance point is found to be at 39.5 cm from the end A when the resistor R is of 12.5 Ω (right gap).
a) Determine the resistance of X (left gap).
b) Determine the balance point of the bridge if X and R are interchanged?
c) What happens if the galvanometer and cell are interchanged at the balance point of the bridge?
(Ans: a) 8.16 Ω b) 60.5 cm )
7) The emf of a standard cell is 1.5V and is balanced by a length of 300 cm of a potentiometer with 10 m long wire. Find the percentage error in a voltmeter which balances at 350 cm when its reading is 1.8 V. 3 (Ans : 2.8571 % )
Long Answer ( LA) ( 4 marks Each)
1) Describe with the help of a neat circuit diagram how you will determine the internal resistance of a cell by using a potentiometer. Derive the necessary formula.
2) Describe how a potentiometer is used to compare the emf’s of two cells by the combination method.
3) State the uses of a potentiometer. Why is a potentiometer preferred over a voltmeter for measuring emf?
