Moving Charges and Magnetism quiz

The Lorentz force on a charge is:

The work done by a magnetic force on a moving charge is:

The radius of the circular path of a charge in a magnetic field is:

The magnetic field at the centre of a circular loop of radius R carrying current I is:

Two parallel wires carrying currents in the same direction:

A galvanometer is converted into an ammeter by connecting:

A voltmeter has:

The torque on a current loop in a magnetic field is:

The magnetic field inside a long solenoid is:

The frequency of revolution of a charged particle in a uniform magnetic field:

Why does a charged particle moving parallel to a magnetic field experience no force? (2 marks)

Why is the soft iron core used in a moving coil galvanometer? (2 marks)

What is a velocity selector? Write the condition for an undeflected particle. (2 marks)

Why should an ammeter have low resistance? (2 marks)

Write the expression for the magnetic dipole moment of a current loop. (2 marks)

Does increasing the current sensitivity always increase the voltage sensitivity? Explain. (2 marks)

Why is the magnetic field outside a long solenoid nearly zero? (2 marks)

State the right hand thumb rule for the field of a straight current. (2 marks)

Why does the kinetic energy of a charged particle not change in a magnetic field? (2 marks)

What is the shape of the path of a charge entering a magnetic field at an angle? (2 marks)

A straight wire 0.5 m long carries a current of 4 A at 30 degrees to a uniform magnetic field of 0.2 T. Find the force on it. (3 marks)

Find the magnetic field at the centre of a single circular loop of radius 5 cm carrying a current of 10 A. (3 marks)

In a velocity selector, E = 3 x 10^4 V/m and B = 0.1 T. Find the speed of the particles that pass undeflected. (3 marks)

A galvanometer of resistance 50 ohm gives full deflection at 2 mA. Find the resistance needed to convert it into a voltmeter of range 0 to 10 V. (3 marks)

An alpha particle (m = 6.64 x 10^-27 kg, q = 3.2 x 10^-19 C) moving at 6 x 10^5 m/s enters a field of 0.2 T perpendicularly. Find the radius of its path. (3 marks)

Read the passage and answer the questions. Charged particles from the Sun approach the Earth and spiral along the Earth's magnetic field lines towards the poles, where they collide with atoms in the atmosphere and produce the aurora. (i) Why do the particles spiral along field lines? (ii) Why are auroras seen mainly near the poles? (iii) Does the magnetic field change the speed of the particles? (5 marks)

Read the passage and answer the questions. An MRI scanner uses a long superconducting solenoid with 2,000 turns per metre carrying a large current to produce a uniform field of about 1.5 T. (i) Write the formula for the field inside a long solenoid. (ii) Find the current needed. (iii) Why is a superconducting coil used? (5 marks)

Read the passage and answer the questions. A moving coil galvanometer has a coil of 50 turns and area 2 x 10^-4 m^2 in a radial field of 0.2 T. The spring constant is 1 x 10^-7 N m per degree. (i) Write the relation between deflection and current. (ii) Find the current sensitivity. (iii) Why is the field made radial? (5 marks)

Read the passage and answer the questions. Two long parallel power cables in a factory carry currents of 100 A each in the same direction and are 10 cm apart. (i) Find the force per metre between them. (ii) Is it attractive or repulsive? (iii) Why must such cables be firmly fixed? (5 marks)

Read the passage and answer the questions. In a mass spectrometer, ions first pass through a velocity selector and then enter a uniform magnetic field, where they move in semicircles of different radii. (i) Why are ions passed through a velocity selector first? (ii) How does the radius depend on mass? (iii) What can be identified from the radius? (5 marks)

State the Biot-Savart law and derive the magnetic field on the axis of a circular current loop, with a diagram. (6 marks)

State Ampere's circuital law and use it to derive the magnetic field of a long straight wire and inside a long solenoid. (6 marks)

Derive the force per unit length between two long parallel current-carrying conductors and define one ampere. (6 marks)

Derive the expression for the torque on a rectangular current loop in a uniform magnetic field and explain the working of a moving coil galvanometer. (6 marks)

Explain with circuit diagrams how a galvanometer is converted into an ammeter and a voltmeter, deriving the required resistances. (6 marks)