Physics

Speed, Velocity and Acceleration

Speed, Velocity and Acceleration

speed = distance/time

acceleration = change in velocity/time

velocity = speed in a specified direction

Boiling

Occurs at a definite temperature called the boiling point when bubbles/vapor form in the liquid and rise.

Mass and Weight

Mass measures the amount of matter in an object

Weight is the force of gravity acting on an object

density = mass/volume

How many forces of change are there in motion

Forces and Change of Motion

Resultant force: gives an acceleration to an object. If object is stationary, it will gain speed. If object is moving, it will gain or lose speed depending on the direction of the force.

Planet in orbit: gravitational force towards sun

Car turning a corner: friction force

Ball on a length of string: string tension

Condensation

Occurs when gas or vapor molecules return to liquid state.

Work

Work is done when a force moves through a distance.
Work done = force x distance moved in direction of force

Melting

Takes place at a definite temperature called the melting point when energy is provided to break bonds between molecules.

Pressure

Pressure on a surface is the force exerted on a given area

The greater the force on a given area, the greater the pressure

The smaller the area the given force acts upon, the greater the pressure

Pressure = force/area

Conduction

Transfer of heat through a material without movement of the material.

Solidification

Occurs when molecules of a liquid returns to solid state. This takes place at freezing point.

Methods of thermal energy transfer

3

How many Changes of State are there

4

How many nature of waves

2

Water Waves

Reflection-The reflected waves are at the same angle to the reflecting surface as the incident waves. Speed, wavelength and frequency are unchanged by reflection.

Refraction- When waves enter, their speed is reduced, Their frequency stays the same so their wavelength is also reduced. the refracted waves change direction.

Diffraction- Speed, wavelength and frequency are unchanged by diffraction.

Power

Power is the rate of doing work

Power = work done/time taken

Lens/Light

All rays of light parallel to the principal axis are refracted by the lens to pass through the principal focus. The distance between F and the optical centre, C, is called the focal length

Dispersion of light: White light is mad up of seven colours. Prism + light = rainbow (Pink Floyd album cover)

Gas pressure

The force exerted by a gas per unit surface area of an object

Electromagnetic Spectrum

1. They can all travel through a vacuum at the same high speed.

2. They show the normal wave properties of reflection

3. They are transverse waves

4. They travel due to moving electric and magnetic fields

These rays include: Gamma rays, X-rays, Ultraviolet (UV)

Magnetism

-Opposite poles attract

-Magnetic field lines always go from N to S

-Magnetic materials are mostly ferrous metals, such as iron, steel and their alloys, along with Cobalt and Nickel.

-Magnetic field can be produced by a permanent magnet or a wire carrying an electric current.

Convection

The transfer of heat by the movement of a fluid

Electromagnetism

-Wire or a coil carrying an electric current produces a magnetic field

-higher current = strong magnetic field

-current reverses = direction of m.f reverses

Remember: right hand grip rule, corkscrew rule

Radiation

Energy transmitted in form of rays or waves or particles.

Electric Current, Electromotive force and Potential Difference

I= current Q= charge t= time

I= Q/t

-Electric current: Flow of charge measured in amps (must be connected in series)

-Electromotive Force: source of electrical energy for a whole circuit, measured in volts

-Potential difference: is a measure of electrical energy transferred in the component, measured in volts. Voltmeter must be connected in parallel with circuit elements.

Resistance

R= resistance in ohms V= Potential Difference

I= current

R= V/I

Greater the resistance, smaller the current

Greater the potential difference, greater the current

Circuit Symbols

Motor effect

A wire carrying a current that creates a magnetic field.

Electromagnetic Induction: when the magnetic field through a circuit changes, a voltage is induced. The induced emf (voltage) increases with the increase of:

-speed of motion of the magnet and circuit

-number of turns on the coil

-strength of magnet

Transformers:

-transformers only work with a.c.

power loss in a cable = p.d. across a length of cable x I (current)

p.d. = I x resistance of cable (R)

power loss = I x R x I = I2R

Transverse waves

ravelling wave in which oscillation is perpendicular to direction of travel

(eg waves, earthquake, electromagnetic wave)

Longitudinal Waves:

Travelling wave in which oscillation is parallel to direction of travel

(eg earthquake, sound)

Frequency: the number of complete cycles which occur in one second (pitch)

frequency = number of cycles/time

Wavelength: the distance between two corresponding points in a successive cycles of a wave

Amplitude: the maximum displacement of a wave from the undisturbed position (volume)

Radiation Rays

Alpha particles: a helium nucleus made up of two protons and two neutrons

-(stopped by thick paper)

-Very high ionising power, very strong

-charge -> +2

Beta particles: a high-speed electron emitted by a nucleus

-(Stopped by a few millimetres of aluminium)

-Ionising effect weak

-charge -> -1

Gamma particles: a high-frequency electromagnetic wave --(Only stopped by many centimetres of lead)

-Ionising effect very weak

-charge -> none

Radioactivity

-Occurs when an unstable nucleus decays and emits one or more of the three types of radiation

-When radioactive particles and molecules in the air collide, the radioactive particles knock electrons out of atoms leaving molecules positively charged (ionisation)

-Background radiation occurs naturally, due to radioactivity in rocks and the air due to cosmic rays.

-Radioactivity is detected by a Geiger counter

Radioactive Decay

-Alpha decay: nucleus loses two neutrons and two protons. nucleon number goes down by 4.

e.g. radium-226 -> randon-222 + a particle

-Beta decay: neutron in the nucleus changes to a proton and an electron, which is emitted at high speed as a beta particle.

e.g. carbon-14 -> nitrogen-14 + b particle

-Gamma decay: gamma rays are usually given off during both alpha decay and beta decay and can be added onto the equations

e.g. carbon-14 -> nitrogen-14 + b particle +g particle

Half-Life

-The average time for half the atoms in a radioactive sample to decay

-There may be small fluctuations but with a large number of atoms in even a small sample, half life is effectively constant.