A small, charged ball (m = 0.1 kg, q = 0.2 C) is connected to a 30.0 m string to

Question

A small, charged ball (m = 0.1 kg, q = 0.2 C) is connected to a 30.0 m string to make a pendulum, as shown at right The whole area around the pendulum is immersed in a magnetic field that points into the plane of the page. The ball is pulled toward the east, as shown below right, so that it rises a vertical distance of 75 cm, and then released. The maximum tension in the string is 1.50 N. After release, the ball moves in a circular path at variable speed. What is the direction of the magnetic field? What is the maximum speed of the ball? What is the strength of the magnetic field? What is the minimum tension in the string?

Explanation / Answer

21) According to Fleming's left hand rule,

The direction of magnetic field is given by forefingrer of left hand. In given problem, ball is pulled in East direction and magnetic fied is inside the plane of paper. So its obvious thing is that direction of magnetic field is in NORTH direction.

22) If angle betweel velocity of the ball and magnetic field is 90 degrees so by using foemula we can calculate the value of v,

F = qVB

By putting the value we will get V = 3.83 m/s

23)

V/r = qB/m

Therefore,

B = mV/qr

And we will get B = 0.0620 tesla

24) After release the ball, it moves in circular path

so minimum tension in the string is,

T - w = mV2/r

where T = mg

so we will get T = 0.0554 N

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