P09.05 DC Motors

The diagram shows a current-carrying wire placed between two magnetic poles. The current is in the direction shown.

What is the direction of the force on the wire?

• towards the bottom of the page

• towards the top of the page

• towards the left-hand side of the page

• towards the right-hand side of the page

A current-carrying coil in a magnetic field experiences a turning effect.

How can the turning effect be increased?

• increase the number of turns on the coil

• reduce the size of the current

• reverse the direction of the magnetic field

• use thinner wire for the coil

The diagram shows a simple DC electric motor which is rotating.

Which change will make the motor rotate more quickly?

• reversing the polarity of the magnets

• reversing the battery

• removing the magnets

• using more powerful magnets

1. A circular coil of wire carries 50mA of current. The coil has 50 turns and an area of 2.0 cm2. A magnetic field of 0.300 T is present, oriented parallel to the plane of the coil. What torque acts on the coil?

• Τ= 2 x 10 ^ -4Nm

• Τ= 1.5 x 10^-4Nm

• Τ= 3.6 x 10^-4Nm

• Τ= 3 x 10^-4Nm

• up, 0.1 x 8 A x 20 cm = 16 N

• down, 0.1 x 8 A x 20 cm = 16 N

• down, 0.1 x 8 A x 0.20 m = 0.16 N

• up, 0.1 x 8 A x 0.20 m = 0.16 N

How does a split ring commutator work?

• Swaps the contact evert full turn, so that the left-hand and right-hand arms of the coil always experience a force in the same direction.

• Swaps the contact evert half turn, so that the left-hand and right-hand arms of the coil do not experience a force in the same direction.

• Swaps the contact evert half turn, so that the left-hand and right-hand arms of the coil always experience a force in the same direction.

Rules for DC motor

• Flemming right hand rule

• Flemming thumb rule

• Flemming left hand rule

• Flamming rotation rule

Operating principle of DC motor formula.

• F=V/R

• F=VR

• F=IV

• F=BiL

Name one factor that does not affect the size of a force in on a current-carrying conductor placed in a magnetic field?

• Gravity

• Magnetic flux density/size of magnetic field

• Size of the current

• Length of the conductor

Name the effect that causes a coil of current-carrying wire in an electric motor to move.

• The electromagnetism effect

• The magnetic effect

• The motor effect