Physics

Question 1

Centre of mass.

Answer 1

At rest, the centre of mass is vertically below the point of suspension.

Question 2

What is the perpendicular distance?

Answer 2

The distance from the line of action of a force to a pivot.

Question 3

Levers.

Answer 3

Levers increase the distance from the pivot at which the force is applied. This means less force is needed to get the same moment. They are know as force multipliers as they reduce the amount of force that’s needed to get the same moment by increasing the distance.

Question 4

How do lenses form images?

Answer 4

By refracting light and changing its direction.

Question 5

Electromagnetic induction.

Answer 5

The creation of potential difference across a conductor which experiences a change in magnetic field.

Question 6

How can potential difference across the ends of a conductor be induced?

Answer 6

By moving the electrical conductor in a magnetic field.

By moving a magnetic field relative to the electrical conductor.

Question 7

What does total internal reflection depend on?

Answer 7

The critical angle of a boundary and the angle of incidence of the light.

Question 8

What is the critical angle?

Answer 8

The angle of incidence above which total internal reflection a happens.

Question 9

Total internal reflection.

Answer 9

Can only happen when light travels through a dense substance to a less dense substance.

Question 10

Optical fibres.

Answer 10

Able to carry light a long way as a result of total internal reflection. The inner core must be denser than the outer core for it to happen.

Question 11

What is the motor effect?

Answer 11

When a current carrying wire in a magnetic field experiences a force.

Question 12

How can the force of a wire be increased?

Answer 12

Increasing strength of magnetic field.

Increasing the size of current in the wire.

Question 13

What happens if a wire runs parallel to the magnetic field?

Answer 13

It won’t experience a force.

Question 14

How can a wire experience a full force?

Answer 14

Wire has to be 90 degrees to the magnetic field.

Question 15

What does reversing the current or the direction of the magnetic field do?

Answer 15

Reverses the force as a result of the motor effect.

Question 16

Images formed by diverging lens.

Answer 16

Smaller.
Right way up.
Virtual.

Question 17

Refraction.

Answer 17

When wave changes direction as it enters a different medium.
It is caused by the change in density from one medium to another.
Waves are only refracted if they hit the boundary at an angle.

Question 18

Refractive index.

Answer 18

The ratio of speed of light in a vacuum to the speed of light in the medium.

Question 19

Partial reflection.

Answer 19

When a wave passes from one medium to another, some of the wave reflects off the boundary and some is transmitted.

Question 20

X ray photographs

Answer 20

They are transmitted through body tissue but absorbed by denser materials like bone.

Question 21

CCDs

Answer 21

Detect x rays and produce electronic signals which are used to form high resolution images.

Question 22

CT scans.

Answer 22

Use high doses of x rays to distinguish small variations in tissue density.

Question 23

Relay switch.

Answer 23

Switch in the low-current circuit is closed.
Current flows through the electromagnet which produces a magnetic field.
The electromagnet attracts the iron contact on the rocker which pivots and closes the contacts in the high-current circuit.

Question 24

Simple d.c. Electric motor

Answer 24

1) A d.c. current flows through the loop and the two side arms which are parallel to the field experience a force.
2) They experience forces which are in opposite directions as the current in each arm is opposite.
3) The loop will rotate around its axis and the forces act one up, one down.
4) When the wire loop reaches a vertical position the forces will still be one up, one down so the loop will get stuck.
5) For the arms to rotate in the same direction, the forces acting on the side arms of the loop need to swap direction.
6) A split ring commutator swaps the contact of the loop energy half turn.

Question 25

How can you increase the speed of a simple electric motor?

Answer 25

Increase the current.

Increase the strength of the magnetic field.

Question 26

How can the direction of the simple electric motor by reversed?

Answer 26

Swapping the poles over.

Swapping the polarity of the direct current supply.