Electromagnetic Induction is one of the most scoring areas in Class 12 Physics and also appears in competitive exams through direct numericals (motional emf, changing flux, induced current) and concept-based reasoning (Lenz’s law, RL time constant effects, energy flow). Mastery of this chapter strengthens your ability to handle both calculation and interpretation questions in CBSE as well as JEE/NEET.
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Minutes
15
Questions
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Marking
Q1. A straight conducting rod of length moves with speed such that its length remains perpendicular to its velocity. The rod moves through a uniform magnetic field ; the velocity makes an angle with the magnetic field. Using , the magnitude of the induced emf between the ends of the rod is
Q2. A conducting rod of length slides without friction on two parallel rails connected at one end by a resistor . The assembly lies in a uniform magnetic field directed into the page. The rod is pulled to the right with constant speed . Calculate the magnitude of the external force required to maintain constant speed (use , and ).
Q3. A circular conducting loop of radius and resistance is lying in a uniform magnetic field directed into the page. The loop's radius is increasing at the rate . At the given instant, the magnitude and direction (as seen by an observer facing the plane of the loop) of the induced current are
clockwise
clockwise
anticlockwise
anticlockwise
Q4. Assertion: For a single-turn circular conducting loop of area , resistance and self-inductance placed in a uniform magnetic field (with constant ), if the loop initially has zero current then for the induced current tends to .
Reason: The induced emf is , and in steady state so the inductive term vanishes; hence Ohm's law gives .
Both assertion and reason are true but the reason does not correctly explain the assertion
Assertion is true but reason is false
Both assertion and reason are true and the reason correctly explains the assertion
Assertion is false but reason is true
Q5. A conducting disc of radius rotates about its central axis with angular speed in a uniform magnetic field perpendicular to the disc. A sliding contact at the center and another at the rim pick off an emf between center and rim. The magnitude of the emf is given by . Its numerical value is
Q6. A straight conducting rod of length moves with speed perpendicular to a uniform magnetic field of magnitude . The magnitude of the potential difference between its ends is (use motional emf ):
Q7. A conducting rod of length slides without friction on parallel conducting rails connected by a resistor , forming a rectangular loop in a region of uniform magnetic field (field into the page). The rod is pulled to the right with constant speed . Assuming steady motion, the magnitude of the external force required to keep the rod moving at constant speed is:
Q8. A single-turn rectangular coil of area rotates with constant angular speed about an axis perpendicular to a uniform magnetic field . The induced emf is with . The rms value of the induced emf is:
Q9. A series circuit with resistance and inductance (time constant ) is connected to a DC battery at . The current is . Find the time (expressed in terms of ) at which the energy dissipated in the resistor from to equals the energy stored in the inductor at time .
Q10. A rectangular conducting loop of dimensions and resistance lies entirely inside a uniform magnetic field (field normal to the plane). The loop is pulled out of the field region until it is completely outside. The magnitude of the total electric charge that flows around the loop during the entire process is:
Q11. A conducting rod of length slides with constant speed on frictionless parallel rails in a region of uniform magnetic field directed into the page. The rod is perpendicular to the rails and completes a closed circuit with a resistor. Neglect resistance of the rod and rails. The magnitude of the motional emf induced across the rod is
Q12. A rectangular loop of height (along ) and width (along ) moves in the direction with constant speed into the region where the magnetic field perpendicular to the loop plane varies as for and is zero for . At the leading edge of the loop is at . For times (i.e., while the loop is partially inside the region) the magnitude of the induced emf in the loop is
Q13. A conducting rod of length slides without friction on parallel rails (forming a closed circuit) connected to a resistor . A uniform magnetic field is perpendicular to the plane. A constant external horizontal force is applied and the rod moves with steady speed . Neglect resistance of the rails and rod. The steady speed is
Q14. Assertion (A): For a rectangular coil of area rotating about a fixed axis with angular acceleration (so its angular speed changes in time), the instantaneous induced emf in the coil is proportional to .
Reason (R): If the coil makes angle with the field, the induced emf is , which depends on the instantaneous angular speed (not on ).
Both A and R are true and R explains A.
Both A and R are true but R does not explain A.
A is false but R is true.
A is true but R is false.
Q15. A conducting rod of mass and length slides without friction on horizontal rails forming a closed circuit of total resistance in a region of uniform magnetic field (into the page). At the rod has speed and there is no external force thereafter. The magnetic damping causes the rod's speed to decay. The time dependence of the rod's speed is