CBSE Class 12 Physics Current Electricity Worksheet Set D

CBSE Class 12 Physics Current Electricity Important Questions (3). Students can download these worksheets and practice them. This will help them to get better marks in examinations. Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

1. What is an electric current? Give the formula to find the electric current. Define its SI unit. 

2. Name the phenomenon in which charges flow from the clouds to the earth through the atmosphere. 

3. Name any two devices where a steady current flow through the device. 

4. Name the layer of the atmosphere in which charged particles exist. 

5. What are conductors? What is the effect of an electric field on a conductor? 

6. State Ohm’s Law. 

7. Define resistance of a conductor. Give the SI unit of resistance. Give the factors on which the resistance of a conductor depends upon. . 

8. Define current density. What is its SI unit of measurement? .

9. What is resistivity of a material? Give the factors on which the resistivity of a material depends upon. How is different from conductivity? 

10. What are the limitations of Ohm’s law? 

11.  Define mobility. Derive an expression to find the mobility of a charged particle.

12. The electron drift arises due to the force experienced by electrons in the electric field inside the conductor. But force should cause acceleration. Why then do the electrons acquired steady average drift sped? 

13. Are the paths of electrons straight lines between successive collisions (with the positive ins of the metal) in the (i) presence of electric field, (ii) presence of electric field? 

Important Questions for NCERT Class 12 Physics Current Electricity

Question. A set of n equal resistors, of value R each, are connected in series to a battery of emf E and internal resistance R. The current drawn is I. Now, the n resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10I.   
The value of n is
(a) 10
(b) 11
(c) 20
(d) 9 

Answer  A

Question. A constant voltage is applied between the two ends of a uniform metallic wire. Some heat is developed in it. The heat developed is double if
(a) both the length and radius of wire are halved    
(b) both length and radius of wire are doubled
(c) the radius of wire is doubled
(d) the length of the wire is doubled

Answer  B

Question. The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 W is    
(a) 0.8 W
(b) 1.0 W
(c) 0.2 W
(d) 0.5 W

Answer  D

Question. A current of 2 A flows through a 2 W resistor when connected across a battery. The same battery supplies a current of 0.5 A when connected across a 9 W resistor. The internal resistance of the battery is    
(a) 0.5 W
(b) 1/3 W
(c) 1/4 W
(d) 1 W 

Answer  B


Question. A student measures the terminal potential difference (V ) of a cell (of emf e and internal resistance r) as a function of the current (I) flowing through it. The slope, and intercept, of the graph between V and I, then, respectively, equal    
(a) –r and e
(b) r and –e
(c) –e and r
(d) e and –r 

Answer  A

Question. A potentiometer wire, 10 m long, has a resistance of 40W. It is connected in series with a resistance box and a 2 V storage cell. If the potential gradient along the wire is 0.1 m V/cm, the resistance unplugged in the box is    
(a) 260 W
(b) 760 W
(c) 960 W
(d) 1060 W

Answer  B


Question. For a cell terminal potential difference is 2.2V when circuit is open and reduces to 1.8 V when cell is connected to a resistance of R = 5 W. Determine internal resistance of cell (r).  
(a) 10 /9Ω
(b) 9 /10Ω
(c) 11 /9Ω
(d) 5 /9Ω

Answer  A

Question. When the power delivered by a 100 volt battery is 40 watts the equivalent resistance of the circuit is :  
(a) 100 ohms
(b) 250 ohms
(c) 300 ohms
(d) 350 ohms

Answer  B

Question. Three copper wires of lengths and cross sectional areas are (l, A), (2 l, A/2) and (l/2, 2A). Resistance is minimum in    
(a) wire of cross-sectional area A/2
(b) wire of cross-sectional area A
(c) wire of cross-sectional area 2A
(d) same in all the three cases

Answer  C


Question. A car battery of emf 12 V and internal resistance 5 × 10–2 W, receives a current of 60 amp from external source, then terminal potential difference of battery is    
(a) 12 V
(b) 9 V
(c) 15 V
(d) 20 V

Answer  C

Question. Three resistances P, Q, R each of 2 W and an unknown resistance S form the four arms of a Wheatstone bridge circuit. When a resistance of 6 W is connected in parallel to S the bridge gets balanced. What is the value of S ?   
(a) 3 W
(b) 6 W
(c) 1 W
(d) 2 W

Answer  A

Question. In a Wheatstone’s bridge all the four arms have equal resistance R. If the resistance of the galvanometer arm is also R, the equivalent resistance of the combination as seen by the battery is    
(a) R /4
(b) R /2
(c) R
(d) 2R

Answer  C


Question. The resistance of each arm of the Wheatstone’s bridge is 10 ohm. A resistance of 10 ohm is connected in series with a galvanometer then the equivalent resistance across the battery will be    
(a) 10 ohm
(b) 15 ohm
(c) 20 ohm
(d) 40 ohm

Answer  A

Question. A resistance wire connected in the left gap of a metre bridge balances a 10 W resistance in the right gap at a point which divides the bridge wire in the ratio 3 : 2. If the length of the resistance wire is 1.5 m, then the length of 1 W of the resistance wire is    
(a) 1.0 × 10^–2 m
(b) 1.0 × 10^–1 m
(c) 1.5 × 10^–1 m
(d) 1.5 × 10^–2 m

Answer  B

Question. In a metre bridge, the balancing length from the left end (standard resistance of one ohm is in the right gap) is found to be 20 cm. The value of the unknown resistance is   
(a) 0.8 W
(b) 0.5 W
(c) 0.4 W
(d) 0.25 W

Answer  D

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