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Question 21M.2.HL.TZ2.7b

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Date May 2021 Marks available [Maximum mark: 4] Reference code 21M.2.HL.TZ2.7b
Level HL Paper 2 Time zone TZ2
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 4]
21M.2.HL.TZ2.7b
(b)

A pendulum with a metal bob comes to rest after 200 swings. The same pendulum, released from the same position, now swings at 90° to the direction of a strong magnetic field and comes to rest after 20 swings.

 

Explain why the pendulum comes to rest after a smaller number of swings.

[4]

Markscheme

bob cuts mag field lines
OR
there is a change in flux linkage ✓

induced emf across bob ✓

leading to eddy/induced current in bob ✓

eddy/induced current produces a magnetic field that opposes «direction of» motion ✓

force due to the induced magnetic field decelerates bob ✓

damping of pendulum increases/there is additional «magnetic» damping ✓


MP4 and MP5 can be expressed in terms of energy transfer from kinetic energy of bob to electrical/thermal energy in bob

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