Q4. Assertion: a copper ring dropped from above onto a fixed vertical bar magnet, falling along the magnet’s axis, has an acceleration less than g as it approaches the magnet. Reason: the current induced in the ring opposes the change in flux, so its force on the ring opposes the motion. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: the induced current makes the ring repel the magnet it is approaching, slowing the fall (reasoned from NCERT page 160).
Q5. In a uniform field pointing into the page, a wire loop of irregular shape is pulled out into a circle, so the area it encloses grows. Which way does the induced current flow, as seen by the reader? (NCERT Exercise 6.2(a))
Anticlockwise. The flux into the page increases, so the induced current makes a field out of the page inside the loop (reasoned from NCERT page 160).
Q6. In a uniform field pointing out of the page, a circular loop is squashed into a narrow straight wire. Which way does the induced current flow, as seen by the reader? (NCERT Exercise 6.2(b))
Anticlockwise. The flux out of the page decreases, so the induced current makes a field out of the page to oppose the decrease (reasoned from NCERT page 160).
Q7. Two loops share a common axis and face each other. A current is switched on in the first, flowing anticlockwise as seen by an observer on the axis beyond the second loop, looking towards the first. Which way does the current induced in the second loop flow, as seen by the same observer?
Clockwise, while the current is rising: opposite to the first loop’s current, so that its field opposes the growing flux, and the two loops repel. Once the current is steady the induced current stops; if the first current were then switched off, the induced current would be anticlockwise and the loops would attract (reasoned from NCERT page 160 and Experiment 6.3).
Q8. A long straight wire passes along the axis of a circular loop, at right angles to its plane, and its current is decreasing at a steady rate. Is a current induced in the loop?
No. The wire’s field lines are circles round the wire, lying in the plane of the loop, so the flux through the loop is zero at every moment and does not change (reasoned from NCERT Eq. (6.1); the setting is NCERT Exercise 6.1(f)).
Q9. A long straight wire in the plane of the page carries an upward current that is increasing. A rectangular loop lies in the same plane to the right of the wire. Which way does the induced current in the loop flow, as seen by the reader?
Anticlockwise. To the right of the wire its field points into the page, and that flux is growing, so the induced current makes a field out of the page inside the loop (reasoned from NCERT page 160).