15 extra multiple-choice questions for Magnetism and magnetic effects of electric current (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
What is the term for the angle between the magnetic meridian at a point and the geographical meridian?
- A. Dip
- B. DeclinationCorrect
- C. Inclination
- D. Horizontal component
Explanation. Magnetic declination is defined as the specific angle formed between the vertical plane of the magnetic axis and the geographic axis at any location on Earth.
Q2
A bar magnet with magnetic dipole moment \(p_m\) is cut into two equal pieces along its axis. What is the new magnetic moment of each piece?
- A. \(p_m\)
- B. \(2p_m\)
- C. \(p_m / 2\)Correct
- D. \(p_m / 4\)
Explanation. When a magnet is cut along its length, the pole strength is halved while the magnetic length remains the same, leading to a magnetic moment that is half the original value.
Q3
According to Coulomb's inverse square law of magnetism, what happens to the force between two poles if the distance between them is doubled?
- A. It is doubled
- B. It is halved
- C. It increases four times
- D. It reduces to one-fourthCorrect
Explanation. The force of attraction or repulsion is inversely proportional to the square of the distance between the magnetic poles, so doubling the distance makes the force four times smaller.
Q4
In which orientation does a magnetic dipole possess maximum potential energy in a uniform magnetic field?
- A. Parallel to the field
- B. Perpendicular to the field
- C. Anti-parallel to the fieldCorrect
- D. At 45 degrees to the field
Explanation. Maximum potential energy occurs when the dipole moment is anti-parallel to the field direction, as the formula \(-p_m B \cos(\theta)\) yields its highest value when the angle is 180 degrees.
Q5
Which of the following is true for diamagnetic materials when placed in a non-uniform magnetic field?
- A. They move from weaker to stronger field parts
- B. They have positive susceptibility
- C. They move from stronger to weaker field partsCorrect
- D. Their atoms have a net magnetic moment
Explanation. Diamagnetic materials have no permanent atomic magnetic moment and are weakly repelled by magnetic fields, causing them to move toward regions of lower field strength.
Q6
According to Curie's law, how does the magnetic susceptibility of a paramagnetic material change as its temperature increases?
- A. It increases linearly
- B. It remains constant
- C. It increases exponentially
- D. It decreasesCorrect
Explanation. Curie's law states that susceptibility is inversely proportional to the absolute temperature, meaning thermal vibrations disrupt the alignment of dipole moments as the material gets hotter.
Q7
What does the area of a hysteresis loop represent for a magnetic material?
- A. Total magnetic flux
- B. Magnetic permeability
- C. Energy lost as heat per unit volumeCorrect
- D. Magnetic susceptibility
Explanation. The area enclosed by the hysteresis curve corresponds to the energy dissipated as heat during one full cycle of magnetisation and demagnetisation for the material.
Q8
Which rule is used to determine the direction of the magnetic field around a straight current-carrying conductor?
- A. Fleming's Left Hand Rule
- B. Right hand thumb ruleCorrect
- C. Tangent law
- D. Newton's Third Law
Explanation. By pointing the thumb in the direction of the current, the encircling fingers indicate the direction of the circular magnetic field lines around the wire.
Q9
What is the magnitude of the magnetic field at the centre of a circular coil of radius \(R\) with \(N\) turns carrying a current \(I\)?
- A. \(\mu_0 NI / 2R\)Correct
- B. \(\mu_0 NI / R\)
- C. \(\mu_0 I / 2\pi R\)
- D. \(2\pi \mu_0 NI / R\)
Explanation. The formula for the magnetic field at the center of a circular current loop is derived from the Biot-Savart law and is proportional to the number of turns and current.
Q10
Under which condition will the magnetic needle of a tangent galvanometer show maximum sensitivity?
- A. When deflection is 0 degrees
- B. When deflection is 90 degrees
- C. When deflection is 45 degreesCorrect
- D. When current is zero
Explanation. The sensitivity of a tangent galvanometer, which measures change in deflection per unit current, reaches its maximum value when the angle of deflection is exactly 45 degrees.
Q11
What is the magnetic dipole moment of an electron revolving in the first orbit of an atom called?
- A. Lorentz unit
- B. Bohr magnetonCorrect
- C. Curie constant
- D. Permeability constant
Explanation. The Bohr magneton is the minimum value of magnetic moment for a revolving electron, used as a fundamental unit to measure atomic-scale magnetic moments.
Q12
A long solenoid has \(n\) turns per unit length and carries a current \(I\). What is the magnetic field deep inside it?
- A. \(\mu_0 nI / 2\)
- B. \(\mu_0 nI\)Correct
- C. zero
- D. \(\mu_0 I / 2\pi n\)
Explanation. Ampere's circuital law shows that the field inside a long solenoid is uniform and depends only on the permeability of free space, the turn density, and the current.
Q13
What is the force experienced by a charge \(q\) moving with velocity \(v\) parallel to a magnetic field \(B\)?
- A. \(qvB\)
- B. \(qvB/2\)
- C. zeroCorrect
- D. \(q/vB\)
Explanation. The magnetic Lorentz force is \(qvB \sin(\theta)\). Since the velocity is parallel to the field, the angle is zero, making the sine value and the resulting force zero.
Q14
What happens when two long, straight parallel conductors carry steady currents in the same direction?
- A. They repel each other
- B. They rotate clockwise
- C. They attract each otherCorrect
- D. No force acts between them
Explanation. Parallel currents in the same direction produce magnetic fields that result in a mutual attractive force between the conductors, while opposite currents cause repulsion.
Q15
How can the voltage sensitivity of a moving coil galvanometer be increased without changing its current sensitivity?
- A. By increasing the number of turns
- B. By increasing the magnetic field
- C. By decreasing the resistance of the coilCorrect
- D. By increasing the area of the coil
Explanation. Voltage sensitivity is the ratio of current sensitivity to the coil resistance. Reducing the resistance while keeping current sensitivity constant directly increases the voltage sensitivity.
Frequently asked questions
How many MCQs are there in Magnetism and magnetic effects of electric current?
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 Magnetism and magnetic effects of electric current 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.
