Physics 2 Unit 3

Front 1

1A) Describe the difference between magnetized and unmagnetized iron.

Back 1

In magnetized iron, the magnetic micro-domains are aligned, thus producing an overall effect. In unmagnetized iron, magnetic micro-domains have a random orientation and therefore cancel.

Front 2

1B) Describe one method of demagnetization.

Back 2

To demagnetize a permanent magnet, the aligned magnetic micro domains must be returned to random orientation, which can be done by heating the iron.

Front 3

1C) Describe what happens when a bar magnet is cut in half.

Back 3

When a bar magnet is cut in half, the magnetic micro-domains retain their orientation, thus producing two smaller magnets; each with a N and S pole.

Front 4

6A) Describe the basic operation of an electric motor based on magnetic torque effects.

Back 4

A current carrying wire in a magnetic field experiences a sideways deflecting force. When formed into a loop, the sides experience equal and opposite forces. Because the forces are not collinear, a magnetic torque is produced.
A D.C. electric motor is a device which changes electric energy into kinetic energy in order to perform useful work. Because there is no counter-spring, when a current flows in the armature, magnetic torque causes the armature to rotate ½ revolutions. At this point the current is reversed, reversing the forces on loop sides resulting in another ½ revolution. An automatic switch composed of a split ring commutator and 2 brushes reverses the current every ½ revolution. This continues until the current is switched off.

Front 5

6B) Describe the basic operation of a galvanometer.

Back 5

A current carrying wire in a magnetic field experiences a sideways deflecting force. When formed into a loop, the sides experience equal and opposite forces. Because the forces are not collinear, a magnetic torque is produced.
A galvanometer is a device used to measure very small currents (micro-currents). When a current flows in the coil, magnetic torque causes the coil to rotate. A spring attached to the coil produces a torque in the opposite direction. The coil rotates until the magnetic torque and the spring counter torque are balanced. A pointer attached to the coil indicates the current on the scale.

Front 6

8A) State Faraday’s Law.

Back 6

The EMF induced on a conducting loop is proportional to the negative time-rate-of-change of the magnetic flux through the loop.

Front 7

8B) Describe two practical examples of Faraday’s Law in use.

Back 7

1. A moving conductor in a magnetic field will experience a retarding force. Induction generates an induced current and an induced magnetic field. The inducted field occurs in a direction to oppose the change which creates it.
2. A changing magnetic field is applied to metal ingot using an AC source to power a coil. This induces currents in the ingots causing them to heat up.