I have No given solutions for these qns but theses are o-level prelim qns from certain sec schools.
The diagram does not tell you how it is connected. Anyway, i believe the solenoid and ac supply connection is the standard kind. The soft iron core is in the solenoid and the aluminum ring is slipped onto the iron core. The actual problem states that the thick Al ring moved up and remained halfway up the iron core when the switch was on for the ac circuit. Account for this observation.
i think i read in a textbook, that Alloys of Al is magnetic, can be used as permanent magnet.
Well,
For qn 1, ANyone knows what is the refractive index of plastic? I think it is around 1.5, same as glass, if u taking plastic as perspex. If so, then A does not hold. What is strange is that in the figure for plastic, there are 2 emergent rays. 1 reflected ray(this is refracted too) and 1 refracted ray.
If incidence angle >critical angle, total internal reflection will occur.
Since for both plastic and glass, the critical angle is about 42, so the incident ray of 45degree will be totally reflected. However, due to the rough surface in this case, the light is dispersed. :dunno:
My answer would be:
D) The plastic surface disperses the light
(Sorry, typo error, no 's' after surface)
If plastic's refractive index is 1.3, then incidence angle of 45 <critical angle of 50, no total internal reflection can occur. ANswer =A (but why still have the internally reflected ray?)
I think for qn2a), the Al ring moved up as it was being magnetised and its induced pole repelled that of the solenoid. It would remain halfway up as radial magnetic field was being induced inside the AL ring.. But i wonder why it won't drop down as the circuit is an ac circuit.
I think for 2b), the AL ring will shoot up faster as it is lighter and magnetised faster and repelled more easily.
2c) The question should be: if u change the ac supply to a dc supply, what will happen to the thick AL ring when u on and off the switch? My answer would be that the AL ring will only move slightly upwards at the instant the switch is on and remain there for the duration of closed circuit. It retained its magnetism. At the instant it is switched off, the AL ring will move down back to its original position as it is now demagnetised. (It is anaglous to electromagnetic induction. Imagine the instant of 'ON' as the instant when a solenoid circuit(with no power supply) with a magnet moving in, the galvanometer will deflect. Think of the duration of switch on as the magnet is stationary inside the solenoid, the galvanometer does not deflect. The instant as the switch is off as the instant u are moving the magnet away from the solenoid.
CAn visualise?)
:sweat:
any comments?