# Magnetostatics Questions and Answers

Practice Magnetostatics Questions and Answers

## Magnetostatics Questions and Answers

Q1. A ring of radius R carries a linear charge density λ. It is rotating with angular speed ω. The magnetic field at its centre is

• (a) 3/2 μoλω
• (b) 1/2 μoλω
• (c) 1/π μoλω
• (d) μoλω

Q2. A coil having N turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. When a current I passes through the coil, magnetic field at the centre is

• (a) μoNI/b
• (b) oNI/a
• (c) μoNI/2(b-a) lnb/a
• (d) μoIN/2(b-a) lnb/a

Q3. The magnetic field inside a current carrying solenoid is B. If its radius is doubled and the current through it also doubles, the magnetic field will be

• (a) B
• (b) 2B
• (c) 4B
• (d) B/2

Q4. Considering magnetic field along the axis of a circular loop of radius R, approximately at what distance from the centre of the loop the field is 1/2√2 times of its value at the centre ?

• (a) 4R
• (b) R
• (c) 3R
• (d) 6R

Q5. Two infinitely long straight wires lie in the x-y plane along x and y axes, respectively. Each wire carries a current i, respectively, in positive direction of x and y axes. The locus of points, where the magnetic field is zero, is

• (a) y² = x
• (b) x = y²
• (c) x-y=0
• (d) x+y=0

Q6. The magnetic field at a point on the axis of an infinitely long solenoid consisting of n turns per unit length wrapped around a cylindrical tube od radius a and carrying current I is given by

• (a) μonI
• (b) μonI/2
• (c) μoanI
• (d) μoI/(2a)

Q7. A circular wire of radius ‘a’ and carrying I is bent along its diameter to make to halves at right angle. What is magnetic field at the centre.

• (a) μoI/a√2
• (b) μoI/a2√2
• (c) μoI/4a
• (d) √2 μoI/3a

Q8. Two coaxial solenoids have radii r1 & r2 and number of turns per unit length n1 and n2 . Magnetic field in the region r<r1 is zero. Here r1<r2. The inner solenoid carries a current I. What is magnetic field in the region r1 < r2 < r3 .

• (a) μon1I
• (b) μon2I
• (c) μo(n2-n1)I
• (d) zero

Q9. A long Solenoid of radius r and number of turns per unit length n carries a current I. A particle of mass m and charge q is thrown perpendicular to the axis (from its centre). Maximum kinetic energy of the particle if it does not hit the windings of solenoid is

• (a) 1/4m μo² n2I2q2r2
• (b) 1/8m μo² n2I2q2r2
• (c) 1/16m μo² n2I2q2r2
• (d) 1/2m μo² n2I2q2r2

Q10. A particle of mass m carrying charge q is moving in a circle in a magnetic field B. According to Bohr’s model, the energy of the particle in the nth level is

• (a) 1/n2 (hqB/πm)
• (b) n(hqB/πm)
• (c) n(hqB/2πm)
• (d) n(hqB/4πm)

Q11. The radius of curvature of the path of a charged particle in a uniform magnetic field is directly proportional to

• (a) charge of the particle
• (b) momentum of the particle
• (c) energy of the particle
• (d) strength of the magnetic field

Q12. A negative test charge is moving near a long straight wire which there is a current. A force will act on the test charge in a direction parallel to the direction of the current it the motion of the charge is in a direction

• (a) towards the wire
• (b) away from the wire
• (c) the same as that of the current
• (d) opposite to that of the current

Q13. If an electron and a proton are moving with the same kinetic energy along the same direction, when they pass through a uniform magnetic field perpendicular to the direction of their motion, which one of the following statement regarding the radii of the trajectories of these two particles in the region of the magnetic field is true ?

• (a) They are the same.
• (b) radius is greater for the electron since it has a higher velocity.
• (c) radius is greater for the proton since it has a higher mass.
• (d) radius is lower for the proton since it has the higher mass.

Q14. A particle of mass m and charge q is thrown into a uniform magnetic field with speed v at θ angle with B. Which of the following statements correct

• (a) pitch of its path is 2πmvsinθ/qB
• (b) radius of its orbit is mvcosθ/qB
• (c) velocity of particle remains constant
• (d) average force on the particle during time 2πm/qB is zero.

Q15. A charged particle P leaves the origin with speed v = vo , at some inclination with the x-axis. There is a uniform magnetic field B along the x-axis. P strikes a fixed target T on the x-axis for a minimum value of B = Bo . P will also strike T if

• (a) B = 2Bo , v = 2vo
• (b) B = 2Bo , v = vo
• (c) B = Bo , v = 2vo
• (d) B = Bo/2 , v = 2vo

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