Topic D2 and D3 Electric and Magnetic Fields [14 marks]

Two parallel wires carry equal currents in the same direction out of the paper. Which diagram shows the magnetic field surrounding the wires?

• A

• B

• C

• D

A charge +Q and a charge –2Q are a distance 3x apart. Point P is on the line joining the charges, at a distance x from +Q.

The magnitude of the electric field produced at P by the charge +Q alone is E.

Determine the electric field at point P.

Two charges Q1 and Q2, each equal to 2 nC, are separated by a distance 3 m in a vacuum. What is the electric force on Q2 and the electric field due to Q1 at the position of Q2?

An ion moves in a circle in a uniform magnetic field. Which single change would increase the radius of the circular path?

• Decreasing the speed of the ion

• Increasing the charge of the ion

• Increasing the mass of the ion

• Increasing the strength of the magnetic field

Magnetic field lines are an example of

• a discovery that helps us understand magnetism.

• a model to aid in visualization.

• a pattern in data from experiments.

• a theory to explain concepts in magnetism.

A current in a wire lies between the poles of a magnet. What is the direction of the electromagnetic force on the wire?

• A

• B

• C

• D

An electron enters a uniform electric field of strength E with a velocity v. The direction of v is not parallel to E. What is the path of the electron after entering the field?

• Circular

• Parabolic

• Parallel to E

• Parallel to v

A negatively charged particle in a uniform gravitational field is positioned mid-way between two charged conducting plates.

The potential difference between the plates is adjusted until the particle is held at rest relative to the plates.

What change will cause the particle to accelerate downwards relative to the plates?

• Decreasing the charge on the particle

• Decreasing the separation of the plates

• Increasing the length of the plates

• Increasing the potential difference between the plates

What is the magnitude of the electric field strength, in descending order, at points X, Y and Z?

• A. YXZ

• B. ZXY

• C. ZYX

• D. YZX

Two long parallel wires P and Q are a distance d apart. They each carry a current. A magnetic force per unit length F acts on P due to Q. The distance between the wires is increased to 2d and the current in Q is decreased to I/2. What is the magnetic force per unit length that acts on P due to Q after the changes?

• F/8

• F/4

• F/2

• F