Important Questions Class 12 Physics Chapter 3 - Current Electricity 2 Marks Questions

CBSE Class 12 Physics Chapter-3 Important Questions – Free PDF Download

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CBSE Class 12 Physics Chapter-3 Important Questions

CBSE Class 12 Physics Important Questions Chapter 3 – Current Electricity

2 Marks Questions

1. Two electric bulbs A and B are marked 220V, 40 w and 220V, 60 W respectively. Which one has a higher resistance?
Ans. We know 
For Bulb A, 
For Bulb B 
Bulb A has higher resistance because its power is less.

2. A Carbon resistor has three strips of red colour and a gold strip. What is the value of resistor? What is its tolerance?
Ans. R R R Gold
Value of the Resistor = 2200
Tolerance = ⁺ 5 %

3. Determine the voltage drop across the resistor R₁ in the circuit given below with E= 60V, ,   and  ?

Ans. are in series
= = 15 
Now are parallel


 = = 6

Now are series
Rnet = 
 Rnet = 6+18 = 24
I= = 
Now voltage drop across

4. Two heated wires of same dimensions are first connected in series and then it’s parallel to a source of supply. What will be the ratio of heat produced in the two cases?

Ans.  Let Resistance of each wire =R

5. V.I graph for a metallic wire at two different temperatures is shown in figure. Which of these two temperatures is higher and why?
Ans. Slope

= Smaller the slope larger is the resistance and since resistance increases with the increases in temperature for metals. Slope is small for 
 temperature is higher

6.A set of n-identical resistors, each of resistance R ohm when connected in series have an effective resistance of X ohm and when the resistors are connected in parallel the effective resistance is Y ohm. Find the relation between R, X and Y ?
Ans. n – resistors connected in series
X = nR —–1)
n – Resistors connected in parallel
Y =  ——2)
Multiply eg. (1) & (2)
XY = 
XY =  

7. Show the resistance of a conductor is given by 

Ans. For a conductor of length  and area A if electric field is applied, Then the digit velocity of electrons is given by

Since I = neAv
I = neA 
I = neA ()

 (

8. Figure shows a piece of pure semiconductor S in series with a variable resistor Rand a source of constant voltage V. Would you increase and decrease the value of R to keep the reading of ammeter (A) constant, when semiconductor S is heated ? Give reasons.

Ans. Resistance of a semi conductor decreases on increasing the temperature, so in order to increase the temperature, s is heated and in order to maintain the ammeter current constant total resistance is the above circuit should remain unchanged, hence value of r has to be increased.

9. Why is constantan or manganin used for making standard resistors?
Ans. The alloys such as constantan or manganin are used for making standard resistors because their resistivities are high and has low temperature coefficient of resistance.

10. What are ohmic and non-ohmic resistors? Give one example of each?
Ans. A resistor which obey ohm’s law are called ohmic resistors for eg -> metals
A resistor which do not obey ohm’s law are called non-ohmic resistors .eg -> semiconductor diode , transistor etc.

11. The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4 , what is the maximum current that can be drawn from the battery?
Ans. Emf of the battery, E = 12 V
Internal resistance of the battery, r = 0.4 Ω
Maximum current drawn from the battery can be calculated as:
The maximum current drawn from the given battery is 30 A.

12. In a potentiometer arrangement, a cell of emf 1.25 V gives a balance point at 35.0 cm length of the wire. If the cell is replaced by another cell and the balance point shifts to 63.0 cm, what is the emf of the second cell?
Ans.Emf of the cell, 
Balance point of the potentiometer, 
The cell is replaced by another cell of emf 
New balance point of the potentiometer, 
The balance condition id given by the relation,



Therefore, emf of the second cell is 2.25 V.

13. What conclusion can you draw from the following observations on a resistor made of alloy manganin?

Ans. It can be inferred from the given table that the ratio of voltage with current is a constant, which is equal to 19.7. Hence, manganin is an ohmic conductor i.e., the alloy obeys Ohm’s law. According to Ohm’s law, the ratio of voltage with current is the resistance of the conductor. Hence, the resistance of manganin is 19.7