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Fundamentals Of Physics
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Short Answer

A particle of charge q moves in a circle of radius r with speed v. Treating the circular path as a current loop with an average current, find the maximum torque exerted on the loop by a uniform field of magnitude B.

The maximum torque exerted on the loop by a magnetic field is τmax=12qvrB

See the step by step solution

Step by Step Solution

Step 1: Given

Radius of a circle is r.

The charge on particle q.

The speed of particle is v.

The magnitude of magnetic field is B.

Step 2: Understanding the concept

Here, we need to use the equations of torque exerted on a current loop by a magnetic field. For the maximum torque, we can consider .

Formulae:

τ=NiAB sin θi=qTT=2πrvA=πr2

Step 3: Calculate the maximum torque exerted on the loop by a magnetic field.

We have the equation for torque exerted on the current loop as

τ=NiAB sin θ

For the maximum torque, sinθ should be maximum, so consider . Here we are also considering the current loop of moving charge, so N=1.

τmax=iAB

Now, the current due to the moving charge can be expressed as

i=qT

But we have the equation of period in terms of velocity as

T=2πrv

So, the equation for current will become

i= qv2πr

Also, the area of cross-section is

A=πr2

Substituting the equation of current and area in the equation of maximum torque, we get,

τmax= qv2πr× πr2τmax=12qvrB

Hence, the maximum torque exerted on the loop by a magnetic field is τmax=12qvrB

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