15 extra multiple-choice questions for Current Electricity (12th Standard Physics, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Which of the following physical quantities is defined as the rate of flow of electric charges through a given cross-sectional area?
- A. Electric potential
- B. Electric currentCorrect
- C. Electrical resistance
- D. Electromotive force
Explanation. Electric current is the measure of how much charge passes through a specific cross-section of a conductor per unit of time.
Q2
By convention, the direction of conventional current in an external circuit is taken to be from:
- A. The negative terminal to the positive terminal
- B. The direction of electron flow
- C. The positive terminal to the negative terminalCorrect
- D. Low potential to high potential
Explanation. Conventional current is defined as the direction in which a positive test charge would move, which is from high to low potential.
Q3
The average velocity acquired by electrons inside a conductor when subjected to an external electric field is called:
- A. Terminal velocity
- B. Angular velocity
- C. Drift velocityCorrect
- D. RMS velocity
Explanation. Drift velocity is the net average speed at which free electrons move through a conductor under the influence of an electric field.
Q4
In the microscopic model of current, the relationship between current (\(I\)) and drift velocity (\(v_d\)) is given by:
- A. \(I = neAv_d\)Correct
- B. \(I = nAv_d / e\)
- C. \(I = n e / Av_d\)
- D. \(I = v_d / neA\)
Explanation. The current is proportional to the number density of electrons, the elementary charge, the cross-sectional area, and the average drift velocity.
Q5
Which of the following describes a device that does not follow a linear relationship between current and voltage?
- A. Ohmic conductor
- B. Copper wire
- C. Non-ohmic deviceCorrect
- D. Carbon resistor
Explanation. Non-ohmic devices, such as diodes, have a complex current-voltage relationship that does not result in a straight line on a V-I graph.
Q6
Electrical resistivity is defined as the resistance offered by a conductor of:
- A. Unit length and any area
- B. Unit area and any length
- C. Unit length and unit area of cross sectionCorrect
- D. Infinite length and zero area
Explanation. Resistivity is an intrinsic property of a material, representing the resistance of a cube of the material with unit dimensions.
Q7
If a carbon resistor has color bands Green, Blue, Orange, and Gold, what is its resistance value?
- A. \(56 \Omega \pm 5\%\)
- B. \(5.6 k\Omega \pm 10\%\)
- C. \(56 k\Omega \pm 5\%\)Correct
- D. \(560 k\Omega \pm 20\%\)
Explanation. Green (5) and Blue (6) provide digits, Orange (\(10^3\)) is the multiplier, and Gold indicates a five percent tolerance level.
Q8
Three resistors of \(R_1\), \(R_2\), and \(R_3\) are connected in parallel. The equivalent resistance \(R_P\) is given by:
- A. \(R_P = R_1 + R_2 + R_3\)
- B. \(1/R_P = 1/R_1 + 1/R_2 + 1/R_3\)Correct
- C. \(R_P = (R_1 R_2 R_3) / (R_1 + R_2 + R_3)\)
- D. \(R_P = \sqrt{R_1^2 + R_2^2 + R_3^2}\)
Explanation. In a parallel circuit, the reciprocal of the equivalent resistance is equal to the sum of the reciprocals of the individual resistances.
Q9
An ideal battery is defined as a source of electromotive force (emf) that has:
- A. Infinite internal resistance
- B. Zero internal resistanceCorrect
- C. Internal resistance equal to load resistance
- D. Varying emf with current
Explanation. An ideal battery maintains a constant terminal voltage equal to its emf because it lacks any internal resistance to impede current.
Q10
Kirchhoff's Current Rule (First Rule) states that the algebraic sum of currents at any junction in a circuit is:
- A. Infinite
- B. Equal to the source voltage
- C. ZeroCorrect
- D. Equal to the total resistance
Explanation. Based on charge conservation, the sum of all currents meeting at a point must be zero, meaning charge cannot accumulate at junctions.
Q11
In a Wheatstone's bridge, the bridge is said to be balanced when the current through the galvanometer is:
- A. Maximum
- B. ZeroCorrect
- C. Equal to the source current
- D. Half of the source current
Explanation. The bridge reaches balance when the potential difference across the galvanometer is zero, resulting in no current flow through it.
Q12
A meter bridge is primarily used to measure:
- A. Unknown electromotive force
- B. Unknown resistanceCorrect
- C. Specific heat of wire
- D. Internal resistance of a cell
Explanation. A meter bridge is a practical application of the Wheatstone network used to find an unknown resistance by locating a balancing length.
Q13
The principle of a potentiometer states that the potential difference across any length of a wire of uniform cross-section is:
- A. Inversely proportional to its length
- B. Directly proportional to its lengthCorrect
- C. Constant regardless of length
- D. Equal to the internal resistance
Explanation. When a steady current flows through a uniform wire, potential drop per unit length is constant, making voltage proportional to length.
Q14
According to Joule's law of heating, the heat produced (\(H\)) in a resistor is proportional to:
- A. The current (\(I\))
- B. The square of the current (\(I^2\))Correct
- C. The inverse of resistance (\(1/R\))
- D. The square root of time (\(\sqrt{t}\))
Explanation. Joule’s law specifies that heat generation depends on the square of the current, the resistance, and the time the current flows.
Q15
The phenomenon in which an electric current is produced in a circuit of two dissimilar metals by maintaining their junctions at different temperatures is:
- A. Peltier effect
- B. Seebeck effectCorrect
- C. Thomson effect
- D. Joule effect
Explanation. The Seebeck effect is the direct conversion of temperature differences into electric voltage at the junction of two different conductors.
Frequently asked questions
How many MCQs are there in Current Electricity?
This chapter has 15 book-back multiple-choice questions, each with the correct answer and a step-by-step explanation.
Are these 12th Standard Physics MCQs free to practise online?
Yes. Every question, answer and explanation here is free, and you can also take them as a timed practice test.
Where can I find the Current Electricity book-back answers?
The correct option for each question is highlighted on this page with a worked explanation, plus a quick answer-key summary at the top.
