A candidate connects a moving coil ammeter A and a moving coil voltmeter V and a resistance R as shown. If the voltmeter reads 20 V and the ammeter reads 4 A, then R is

• equal to 5Ω

• greater than 5Ω

• less than 5Ω

• none of these

Two identical galvanometers are taken, one is to be converted into an ammeter and other into a milliammeter. The shunt of milliammeter compared to ammeter is

• less

• more

• zero

• none of these

If the vibrations of a string are to be increased by a factor of two, the tension in the string should be made

• twice

• four times

• eight times

• half

Which of the following has the minimum resistance?

• Voltmeter

• Millivoltmeter

• Ammeter

• Milliameter

In a cyclotron, if a deuteron can gain the energy of 40 MeV, then a proton can gain the energy of:

• 40 MeV

• 80 MeV

• 20 MeV

• 60 MeV

An electron, moving in a uniform magnetic field of induction of intensity B, has its radius directly proportional to:

• its charge

• magnetic field

• speed

• none of these

287.

A uniform magnetic field is at a right angle to the direction of motion of proton. As a result, the proton describes a circular path of radius 2.5 cm. If the speed of proton is doubled then the radius of the circular path will be :

• 0.5 cm

• 2.5 cm

• 5.0 cm

• 7.5 cm

An electron accelerated through a potential difference enters into a uniform transverse magnetic field and experience a force F. If the accelerating potential is increased to 2V, the electron in the same magnetic field will experience a force :

• F

• F/2

• $\sqrt{2} \mathrm{F}$

• 2F

The certain amount of current when flowing in a properly set tangent galvanometer produces a deflection of 45°. The current be reduced by a factor of ✓3, the deflection would :

• decrease by 30°

• decrease by 15°

• increase by 15°

• increase by 30°

A wire carrying current I and other carrying 2I in the same direction produce a magnetic field B at the mid-point. What will be the field when 2I wire is switched off?

• B/2

• 2B

• B

• 4B