Question

An 0.80-m aluminum bar is held with its length parallel to the east-west direction and dropped from a bridge. Just before the bar hits the river below, its speed is 23 m/s, and the emf induced across its length is 5.5 x 10-4 V. Assuming the horizontal component of the Earth's magnetic field at the location of the bar points directly north, (a) determine the magnitude of the horizontal component of the Earth's magnetic field.(b) state whether the east end or the west end of the bar is positive.

Answer 1

Answer:

a) $B=2.9891\times 10^{-5}\,T$

b)  west end of the bar is positive.

Explanation:

Given:

• emf induced in the bar, $\epsilon=5.5\times 10^{-4}\,V$

• length of the bar, $l=0.8\,m$

• velocity of the bar at the given instant, $v=23\,m.s^{-1}$

(a)

The magnitude of the horizontal component of the Earth's magnetic field(B):

We know:

$\epsilon=B.l.v$

$5.5\times 10^{-4}=B\times 0.8\times 23$

$B=2.9891\times 10^{-5}\,T$

(b)

Using Fleming's left hand rule we determine that the current is flowing towards east end of the bar i.e. west end of the bar is positive.