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Flashcards in Physics Deck (26):

Centre of mass.

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


What is the perpendicular distance?

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



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.


How do lenses form images?

By refracting light and changing its direction.


Electromagnetic induction.

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


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

By moving the electrical conductor in a magnetic field.
By moving a magnetic field relative to the electrical conductor.


What does total internal reflection depend on?

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


What is the critical angle?

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


Total internal reflection.

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


Optical fibres.

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.


What is the motor effect?

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


How can the force of a wire be increased?

Increasing strength of magnetic field.
Increasing the size of current in the wire.


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

It won't experience a force.


How can a wire experience a full force?

Wire has to be 90 degrees to the magnetic field.


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

Reverses the force as a result of the motor effect.


Images formed by diverging lens.

Right way up.



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.


Refractive index.

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


Partial reflection.

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


X ray photographs

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



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


CT scans.

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


Relay switch.

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.


Simple d.c. Electric motor

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.


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

Increase the current.
Increase the strength of the magnetic field.


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

Swapping the poles over.
Swapping the polarity of the direct current supply.