# Moving Charges and Magnetism - Online Test

Q1. cyclotron frequency of a charged particle having charge q and mass m in a cyclotron producing magnetic field B is
Answer : Option B
Explaination / Solution:

A particle of charge q moving with a speed v on entering a magnetic field B, experiences magnetic Lorentz force which acts as a centripetal force.

here, $\nu$ is the cyclotron frequency.

Q2. what is common to both biot savart law and ampere's law
Answer : Option D
Explaination / Solution:

Both Biot- Savart’s lawand ampere’s circuital law$I$deal with the consequences of steady current. Ampere’s circuital law is to Biot- savart’s law as is Gauss’s law to Coulomb’s law in electrostatics.

Q3. According to Ampere's circuital law
Answer : Option A
Explaination / Solution:

the expression for Ampere’s circuital law is where I is the current included in the surface bounded by the line integral.

Q4. The magnetic field at the center of a solenoid coil having n turns and carrying a current I in air is
Answer : Option B
Explaination / Solution:

The magnetic field at the centre of a solenoid with air core is .where,is the permeability of free space, n the number of turns per unit length and I is the current flowing through the solenoid.

Q5. The magnetic field at the center of a toroidal coil having n turns,radius r and carrying a current I in air is
Answer : Option B
Explaination / Solution:

A toroid is a solenoid wound on itself. The magnetic field exists only in the region of the hollow circular ring which has the turns of wire wound on it. Using Ampere’s circuital law,
Q6. For two parallel wires carrying currents Ia and Ib seperated by a distance d, the magnitude of force acting on length L of any of the wires is
Answer : Option B
Explaination / Solution:

The conductor carrying current Ib is placed in the magnetic field created by the conductor carrying current ${I}_{a}$. The force it experiences
Q7. A rectangular current-carrying coil having n turns,area A and a current I flowing, in a uniform magnetic field B experiences a maximum ,torque equal to
Answer : Option A
Explaination / Solution:

The torque experienced by a current carrying conductor placed in a magnetic field is given by .This has a maximum value when;
Q8. magnetic moment of a single-turn current loop of aluminium wire of area A,carrying a current I in a wire of diameter d is
Answer : Option B
Explaination / Solution:

The torque experienced by a current carrying coil of N turns placed in a magnetic field$\stackrel{}{\tau }$.For N =1, Comparing with torque experienced by a electric dipole

Q9. magnitude of the magnetic moment of an electron of mass me if e is the charge on the electron and angular momentum is l, is
Answer : Option A
Explaination / Solution:

The electron moving in a circular orbit of radius r with a speed v and time period T constitutes a current .since,thereforeThe orbital magnetic moment of the electron The angular momentum of the electron ,sincetherefore,
Q10. In a moving coil galvanometer the current through the coil produces a torque to turn the coil. The torque is balanced by
Answer : Option B
Explaination / Solution:

In a moving coil galvanometer, the coil is pivoted on a helical spring. When current passes through the coil, it experiences a torque and deflects. A restoring torque is set up in the helical spring which tries to restore the coil to its original position.