Unformatted text preview: PHY2054 Spring 2007 18. The ﬁgure shows two concentric circular wire loops. The current in the outer loop is clock-
wise and decreasing at aeonstantr‘ate. The induced current in the inner loop is (CW = clockwise and CCW = counterclockwise) 08‘
@ CW, constant \i“ i a l m
(2) cw, increasing V. (V) (a M Ml we, (3) CCW, decreasing
Meow, increasing The current in the outer loop decreases at a constant rate, so the B ﬁeld in the downward direc-
tion is decreasing at a constant rate. By Lenz’ law, the current induced in the inner loop must be CW (to offset decrease in downward ﬂux) and Faraday ’s law says 1%
rate of chan of flux is * “‘—‘ 19. A metal rod slides along two parallel conductors at speed v = 4.9 cm/s while immersed in a
uniform magnetic ﬁeld B = 1.85T, as shown. If the conductor separations are as shown and the
total resistance of the bar and rails is 5.69, the magnitude of the induced current (in mA) and its
direction will be (CW = clockwise and CCW = counterclockwise): 2.75, CCW
( ) 5.18, CW
(3) 18.0, CW
(4) 15.4, CCW
(5) zero induced current The inducedemfis BLv, where B = 1.85 Tis the Bﬁeld, L = 0.17 m is the width andv = 0.049
m/s is the velocity of the bar. This yields emf = 0.0154 V. The current is 0. 0154 / 5.6 = 2.75 mA and is CCW by Lenz’ law. 20. A multi~loop coil of wire forming a closed circuit is placed within a' magnetic ﬁeld. Which
situations will cause a current to ﬂow in thelcoi‘l? ‘ (A) coil rotating in constant ﬁeld ..
coil accelerating in constant ﬁeld '
' in variable ﬁeld cod movm at constant veloci (2’)“ A only
(33/ B only
(4) C only
(5) A, B and C ...
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- Spring '09