The motor effect (F = B I l) and Fleming's left-hand rule

Question 1

Why does the coil of a simple dc motor keep spinning in the same direction?

• A. The magnets swap poles
• B. The battery turns over
• C. Friction pushes it
• D. A split-ring commutator reverses the current every half turn

Question 2

A wire 0.4 m long carrying 10 A sits at right angles to a magnetic field of 0.5 T. What is the force on the wire, in N?

Answer N

Question 3

A 0.2 m wire carrying 5 A at right angles to a magnetic field feels a force of 0.5 N. What is the magnetic flux density, in T? (Give 2 decimal places.)

Answer T

Question 4

In Fleming's left-hand rule, what do the first finger, second finger and thumb represent?

• A. field, current, motion (force)
• B. current, field, motion
• C. voltage, resistance, power
• D. motion, current, field

Question 5

A wire 0.5 m long carrying 10 A sits at right angles to a magnetic field of 0.5 T. What is the force on the wire, in N?

Answer N

Question 6

A 0.1 m wire carrying 2 A at right angles to a magnetic field feels a force of 0.6 N. What is the magnetic flux density, in T? (Give 2 decimal places.)

Answer T

Question 7

Why does the coil of a simple dc motor keep spinning in the same direction?

• A. A split-ring commutator reverses the current every half turn
• B. The magnets swap poles
• C. Friction pushes it
• D. The battery turns over

Question 8

A wire 0.05 m long carrying 5 A sits at right angles to a magnetic field of 0.5 T. What is the force on the wire, in N?

Answer N

Question 9

A 0.5 m wire carrying 2 A at right angles to a magnetic field feels a force of 0.2 N. What is the magnetic flux density, in T? (Give 2 decimal places.)

Answer T

Question 10

Electric car motors and loudspeakers both rely on which effect?

• A. the greenhouse effect
• B. the motor effect: a force on a current in a magnetic field
• C. static electricity
• D. the photoelectric effect

Question 11

A wire 0.2 m long carrying 2 A sits at right angles to a magnetic field of 0.25 T. What is the force on the wire, in N?

Answer N

Question 12

A 0.1 m wire carrying 4 A at right angles to a magnetic field feels a force of 0.1 N. What is the magnetic flux density, in T? (Give 2 decimal places.)

Answer T

Question 13

Which change would NOT increase the force on a current-carrying wire in a magnetic field?

• A. using a stronger magnet
• B. turning the wire so it is parallel to the field
• C. increasing the current
• D. having a longer length of wire in the field

Question 14

A wire 0.1 m long carrying 3 A sits at right angles to a magnetic field of 0.5 T. What is the force on the wire, in N?

Answer N

Question 15

A 0.5 m wire carrying 4 A at right angles to a magnetic field feels a force of 0.2 N. What is the magnetic flux density, in T? (Give 2 decimal places.)

Answer T

Question 16

In Fleming's left-hand rule, what do the first finger, second finger and thumb represent?

• A. voltage, resistance, power
• B. field, current, motion (force)
• C. motion, current, field
• D. current, field, motion