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201.

Two proton beams going in the same direction repel each other whereas two wires carrying currents in the same direction attract each other. Explain.A. potential difference between themB. mutual inductance between themC. electric force between themD. magnetic force between them

Answer» Correct Answer - D
The parallel wires carrying current in the same direction attract each other because mangnetic forces on the two wires each other.
Discussion
202.

An `alpha` particle travels in a circular path of radius `0.45 m` in a magnetic field `B = 1.2 Wb//m^(2)` with a speed of `2.6xx10^(7) m//sec`. The `alpha` particle isA. `1.1xx 10^05 s`B. `1.1 xx 10^-6 s`C. `1.1 xx 10^-7s `D. `1.1 xx 10^-8 s`

Answer» Correct Answer - C
`T=(2pim)/(q B)=(2pi mr)/(mv)=(2pi r)/(v)`
Discussion
203.

A charged particle enters a magnetic field `H` with its initial velocity making an angle of `45^(@)` with `H`. The path of the particle will beA. straight lineB. a circleC. an ellipseD. a hellix

Answer» Correct Answer - D
The component of velocity perpendicular to H will make the motion circular while that parallel to H will make it move along a straight line the two together will make the motion helical
Discussion
204.

What uniform magnetic enter a magnetic field applied perpendicular to a beam of electrons moving at `1.3xx10^(6) ms^(-1)` is required to make the electrons travel in a circular arc of radius 0.35 mA. `21 xx10^(-5) T`B. `6xx10^(-5)T`C. `2.1 xx 10^(-5)T`D. `6xx10^(-5)T`

Answer» Correct Answer - C
Radius `r=(mv)/(qB)`
or magnetic due to moving electron `B=(mv)/(qr)`
`=(9.1xx10^(-31)xx1.3xx10^(6))/(1.6xx10^(-19)xx0.35)=2.1xx10^(-5)T`
Discussion
205.

A particle of mass `M` and charge `Q` moving with velocity `vec(v)` describe a circular path of radius `R` when subjected to a uniform transverse magnetic field of induction `B`. The work done by the field when the particle completes one full circle isA. `(mv^(2))/(R )2pi R`B. zeroC. `BQR pi R`D. `BQv 2pi R`

Answer» Correct Answer - B
When particle descirbes circular path in a magnetic field its velocity is always perpendicular to the magnetic force thus work done by the fielf is zero
Discussion
206.

The velocity of two `alpha`-particles A and B in a uniform magnetic field is in the ratio of `1:3`. They move in different circular orbits in the magnetic field. The ratio of radius of curvature of their paths isA. `1:2`B. `1:3`C. `3:1`D. `2:1`

Answer» Correct Answer - B
`(r_1)/(r_2)=(v_1)/(v_2)=(1)/(3)`
Discussion
207.

A galvonometer of resistance `20 Omega` gives a full scale deflection with a current of 0.04A is passed through it. It is derised to convert it into an ammeter of range 20A . The only shunt available is `0.05 Omega` . The resistance that must be converted in series with the coil of the galvonometer isA. `2.95 Omega`B. `4.95 Omega`C. `4.35 Omega`D. `4.25Omega`

Answer» Correct Answer - B
In parallel combination potential is same
`therefore I_g (G+R)=(I-I_g)S`
`0.04(20+R)=(20-0.04)0.05`
`therefore R=4.95Omega` .
Discussion