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Unformatted text preview: 4 ©Prep101 Phys1026 April Exam Solutions = (6.0A)(0.05m) / [π (1.0A)] – (0.05m)
= 0.045m
r = 4.5cm
Using RHR, the direction of B due to the long wire is into the page, therefore, the
direction of B due to the loop must be out of the page, to satisfy the Bnet of zero, and the
current should flow counterclockwise. Solutions will be posted at www.prep101.com/solutions 35 ©Prep101 Phys1026 April Exam Solutions 10. INDUCTION AND INDUCTANCES
Question 1 Solution This is a question about energy transfer and power in a changing loop. Key point: The power dissipated in the loop (in the resistor) is equal to the work
done by the force
Ploop = Pforce
The power dissipated in the loop can be found from ε= dΦ d ( BA)
ds(t)
=
= Ba
= Bav
dt
dt
dt ∴I = and ε = IR Bav
R ∴ P = vI = I 2 R = B2a 2 v 2
R so
Ploop= PForce
B2a2v2/R = Fv
F = B2a2v/R Solutions will be posted at www.prep101.com/solutions 36 ©Prep101 Phys1026 April Exam Solutions Question 2 Answer
a) As it enters the field
Call x the distance that the leading edge has penetrated into the strong B field region. The flux through the loop increases in time so the voltage: is induced in the coil, producing a counterclockwise currentthat creates its own B – field
that opposes this change.
b) The flux through the loop is constant when the loop is wholly inside the B – field
region, therefore the induced emf is zero.
c) The emf is the same size as in part a) but in the opposite direction, clockwise. Solutions will be posted at www.prep101.com/solutions 37 ©Prep101 Phys1026 April Exam Solutions Question 3 Solution a) The current will be moving down the metal bar. Use the righthand rule; your fingers
point in the direction of the magnetic field, into the page. Your thumb points in the
direction of the current along the bar, which is down. Your palm is facing to the right
which is the direction of the magnetic force which causes the bar to move. The bar moves
to the right.
b) The bar moves to the right and this increases the flux going into the page. The
magnetic field generated by the induced current needs to oppose this change in flux, so
the magnetic field generated by the induced current needs to point out of the page. By the
other righthand rule, this means the current is going counterclockwise around the closed
circuit. Solutions will be posted at www.prep101.com/solutions 38 ©Prep101 Phys1026 April Exam Solutions Question 4
Solution a) The induced emf is given by
ε= − dΦ B
dt The magnetic flux is
ΦB = BA
and the only a...
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This document was uploaded on 03/21/2014 for the course PHYSICS 1402 at UWO.
 Winter '14
 Prof.PaulineBarmby
 Physics

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