Physics Model answers

Fission

Slow moving neutron is absorbed by a nucleus making it unstable causing it to split into two daughter nuclei. Releases moving neutrons and lots of energy.

Fusion

Two smaller nuclei joining to form one large nucleus releasing a lot of energy.

Doppler

When the object emitting a wave moves towards you the wavelength decreases and because wave speed is constant and frequency = wave speed / wavelength frequency increases. Causes high pitch sound.

Red Shift

Doppler effect but with light emitted from hydrogen isotopes in galaxies.

Finding Specific heat capacity

Delta c= Q/m x delta T. Set up a circuit with a heater and voltmeter in parallel around it.
Also have an ammeter.
Measure mass of item using a balance.
Place a thermometer on the object and measure the change in temperature.
To find Q do voltmeter reading times by ammeter reading times by time taken for temperature to be reached.
Put all results into formula.

Cosmic Micro Background Radiation - CMBR

CMBR comes from all directions.
It began as gamma radiation, but its wavelength has increased as the universe expanded making it microwaves 

Evolution of a star (High mass-relative to the sun)

Nebula collapses under gravity forming a main sequence star.
MSS starts fusing hydrogen until no more is left.
This causes it to collapse on itself until larger elements like helium begin to fuse.
This causes high mass star to expand until it becomes a red super giant.
Once iron runs out the star collapses on itself imploding which causes a supernova.
This leaves a black hole or neutron star.

Evolution of a star (Low mass-relative to the su

Same steps as high mass but doesn’t form a red super giant. Instead, it forms a red giant.
Here outer layers keep expanding which causes them to cool and form a planetary nebula.
The core remains intact.

Generator

A coil rotates which cuts though magnetic field lines inducing a voltage.
If the coil is connected to a circuit, then an alternating current is induced.

Motor

When a current flows in a wire this creates a magnetic field around the wire this magnetic field interacts with the field from the permanent magnet this produces a force on the wire which moves it.
The split ring commutator changes the direction of the current every half turn this reverses the direction of the forces allowing the coil to continue spinning. 

Transformers

An alternating current in the primary coil creates a changing magnetic field.
The magnetic field is linked by a soft iron core to the secondary coil the secondary coil cuts the magnetic field lines inducing a voltage in the secondary coil.
The strength of the induced voltage depends on the number of turns in both the primary and secondary coil. 

National grid

A series of transformers and wires that transport electrical energy to consumers across the country.

Induction (Voltage)

When a conductor cuts through magnetic field lines creating (inducing) a voltage.

Convection

Happens in fluids. As particles heat up, they gain KE and spread out more.
This causes them to lose density and rise.
As they rise, they cool, increasing density and eventually they fall again. 

Conduction

Transfer of heat through direct contact.
When object touches a hot item particles gain kinetic energy causing them to vibrate more.
They collide with neighbouring particles causing a gradual transfer of heat along the object.
Happens faster in metals as they have free electrons which can move along the object faster colliding with particles at the opposite end.

Radiation

Transfer of energy via waves, can happen in a vacuum as particles aren’t needed. 

Loudspeaker

An alternating current from the source passes thought the coil in the speaker this current is constantly changing direction and magnitude creating a changing magnetic field around the coil.
The field interacts with the magnetic field from the permanent magnets creating a constantly changing force on the coil.
This causes the coil to vibrate in and out moving the cone. This causes vibrations in the air which we hear as sound waves. 

Air bags/ Safety systems

Force = change in momentum/ time.
Safety features increase the time taken to reach the same momentum if its constant.
This means change in momentum stays the same but time increases, creating less of a force on the person which is safer.

Critical angle

Angle at which angle of refraction is 90 degrees.

Electrostatic friction

When you rub an object depending on the material and it gains or loses electrons causing it to gain a charge.

Electrostatic induction

If an object has a negative charge, it repels the closest electrons in the wall since same charges repel, this means that the wall is left with an overall positive charge and because the charges are opposite the object is attracted to the wall.

Moment

In an object is in equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments.

Equilibrium

When moments are equal and opposite on an object (balanced).
- If there is a resultant moment the object will rotate in the direction of the resultant moment.

Newtons 3^rd law

All forces have an equal and opposite force. They are the same type of force and the same magnitude they act on different objects and in opposite directions.

Conservation of momentum

Moments before must be equal to after.

Electromagnet

Magnet made by running current through a coil of wire (often around a metal core).