Magnetism and EMI

The diagram shows a current I in a vertical square coil.

The coil can rotate about an axis OO’.

The plane of the coil is at right angles to a uniform horizontal magnetic field of flux density B

Which statement is correct?

• The forces on the vertical sides of the coil are equal in magnitude

  and opposite in direction.

• A non-zero couple acts on the coil.

• No forces act on the horizontal sides of the coil.

• The forces on all sides of the coil act toward the centre of the coil.

When an electron is moving at a speed v perpendicular to a uniform magnetic field of flux density

B, it follows a path of radius R.

A second electron moves at a double the speed and perpendicular to a uniform magnetic field of flux density 4B.

What is the radius of the path of the second electron?

• R/8

• R/2

• 2R

• 8R

Three identical magnets P, Q and R are released simultaneously from rest and fall to the ground

from the same height.

P falls directly to the ground.

Q falls through the centre of a thick horizontal conducting ring.

R falls through a similar ring that has a gap cut into it.

• P and R arrive together, followed by Q.

• P and Q arrive together, followed by R.

• P arrives first, followed by Q which is followed by R.

• All three magnets arrive simultaneously.

Different magnetic fields are present in the two chambers shown. A particle enters the first

chamber at a velocity of 80 m s–1 and is deflected into a circular path of radius 200 mm

In the second chamber it follows a circular path of radius 100 mm

The particle leaves the second chamber at a speed of

• 20m/s

• 40m/s

• 80m/s

• 160m/s

A current-carrying conductor with length l is placed at right angles to a magnetic field with

magnetic flux density B. The graph shows how the force on the wire varies with the current

passing through it.

• B

• Bl

• L/B

• B/L

The beam is produced by accelerating electrons through a potential difference of 250 V.

The electric field strength is 1.4 × 10*4 V m−1. The magnetic flux density is

1.5 × 10*−3T.

A uniform electric field of electric field

strength E is applied given that the electric and magnetic forces on the electrons are equal and

in opposite directions. Calculate the value of the charge/ mass (e/m) for the electron using this data.

• 1.7x10*21C/kg

• 2.7x10*11C/kg

• 1.7x10*11C/kg

• 1.7x10*-11C/kg