Important Questions for Class 12 Physics Chapter 3 focus on Current Electricity, one of the most scoring and numerical-based chapters in the CBSE Class 12 Physics syllabus.
Class 12th chapter Current Electricity covers electric current, drift velocity, resistivity, combination of resistors, Wheatstone bridge, meter bridge, and potentiometer. Practicing Current Electricity Class 12 Important Questions ensures speed, accuracy, and conceptual clarity before the board exam.
Current Electricity Class 12 Important Questions
Students must thoroughly solve Current Electricity Class 12 Solutions, especially circuit-based problems involving Kirchhoff’s laws, Wheatstone bridge, and potentiometer.
Below are the Important Questions for Class 12 Physics Chapter 3 which cover short answers, long answers, derivations, and numerical problems.
1. Which element is used in electric heater? [Foreign 2017]
(A) Copper
(B) Platinum
(C) Tungsten
(D) Nichrome
Sol. (D)
Nichrome is used in electric heater because of the following reasons:
1. Its melting point is high.
2. Its resistivity is large.
3. It is not easily oxidised by the oxygen of the air when heated.
Thus (D) is correct option.
2. Dimension of electromotive force (e.m.f.) is. [Delhi 2002]
3. A current of 10 ampere flows in a wire for 10 sec. It potential difference across the wire is 15 volt, the work done will be [OD 2012, SQP 2004]
(A) 150
(B) 75 J
(C) 1500 J
(D) 750 J
4. What is electromotive force? [OD 2017]
Sol. The emf of a source may be defined as the work done by the source in taking a unit positive charge from its lower potential terminal to the higher potential terminal. Or, it is the energy supplied by the source in taking a unit positive charge once round the complete circuit. It is equal to the terminal p.d. measured in open circuit.
5. Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel with each other access an external resistance R. What is the current through this resistance? [Comp 2021]
6. Why alloys like constantan or manganin are used for making standard resistors? [OD 2017]
Sol. Use of alloys like constantan or manganin in making standard resistance coils. This is because of the following reasons:
1. These alloys have high value of resistivity.
2. They have very small temperature coefficient. So, their resistance does not change appreciably even for several degrees rise of temperature.
3. They are least affected by atmospheric conditions like air, moisture, etc.
4. Their contact potential with copper is small.
7. Express Ohm's law in vector form. [OD 2019]
8. Using theory of drift velocity, express Ohm's law. [OD 2018, Foreign 2004]
9. V-I graph for two identical conductors of different materials A and B is shown in the figure. Which one of the two has higher resistivity? [Delhi 2011]
Sol. The resistivity of material B is higher.
Reason: If the same amount of the current flows through them, then VB > VA and from Ohm's law RB > RA. Hence, the resistivity of the material B is higher.
Most Repeated Questions from Current Electricity
Along with the Current Electricity Class 12 Question Answers, students must focus on:
-
State and explain Ohm’s Law.
-
Derive the relation between current density and drift velocity.
-
Explain combination of resistors in series and parallel.
-
State Kirchhoff’s laws and apply them to a circuit.
-
Explain the principle and working of a potentiometer.
Common Mistakes Students Make in Current Electricity
To score well in 12th Physics, avoid these common errors from this chapter:
-
Applying Kirchhoff’s rules incorrectly.
-
Forgetting sign conventions in loop equations.
-
Ignoring units in final answers.
-
Making mistakes in resistor combinations.
-
Writing incomplete derivations without explanation.
Avoiding these mistakes can help secure full marks in Current Electricity.