Physics

The less energy an appliance wastes the more efficient it is.

1) 48,000W runs for 2 minutes. How much energy will it transfer?

48,000W times 120 = 576 0000

2) An electric peppar grinder is supplied with 55J of energy by battery. Wasted 25J of this energy. How much energy is transferred usefully and what is peppar grinders efficiency?

55J energy, 25J wasted, 30J transferred usefully   30 divided by 55 = 0.54 effciency 

-How electricity is transferred from power stations to home

Step up transformers increase voltage which decraeses current to reduce energy loss.

Step down transformers increase current and decraese voltage so it is safe to use at home.

Voltage is amount of energy and how fast it flows.

Power = Current times voltage 

Gamma is a wave and has no mass

Alpha is + charged and has greatest mass

Beta is - charged

Range in air

Alpha- Few cm                           Beta- 1 metre                             Gamma- Whole universe

Beta and gamma dangerous but Alpha is more damage. Can cause cancer.

Alpha decay

Rn --------> Po   + a

Beta decay

Po ---------> Rn   + e

Radioactive decay rate = half life, half of atoms

Half life of Uranium ( 1 million years )

1000 atoms

500 atoms

250 atoms

125 atoms

- Ionising radiation enter living cells and damage them.

Irradiation

Radioactive from material can damage cells of person directly.

Not radioactive source

Contamination

Swallowed/breathed in, while inside body radiation emits and causes damage.

Radioacitve source

The effect on body when low radiation is may be chance of cancer.

When high radiation bone marrow dosen't work normally.

Contamination is more dangerous than irradiation because it is inside body and you are radioactive.

Transverse waves - Light 

Ocillations are perpendicular to direction of energy transfer

Longitudinal waves - Sound 

Ocillations are parallel to direction of energy transfer

Amplitude is height of wave measured from the middle.

Wave length is distance from a point on one wave to the equivelent point on the next wave.

Frequency is number of waves produced each second.

Period is time taken to produce one wave

Frequency and period

The higher frequency, the shorter wave period and longer wavelength.

- Are transverse waves

- Radiowaves (1m-10m) - Microwaves (10m) -Infrared (10m) - Visible light (10m) -Ultra violet (10m) -X-rays (10m) -Gamma rays (10m)

High frequency                             Low frequency

High energy                                  Low energy

All travel at same speed in a vaccum.

Hazard is higher radiation so more damage to body.

1) A wave has velocity of 200 m/s and a wavelength of 2cm. Calcualte frequency of wave?

2cm divided by 100 = 0.02m  Convert to metres first

200 divided by 0.02 = 10 000 Hz

-Bending of waves when they pass from one material to another material.

Light slows and ray bends towards the normal.

Light speeds up and ray bends away from normal.

Wavefonts

Showing all points on a wave that are in same position as each other after given number of wavelengths.

They refract as they cross from deep water to shallow water.

Causes are:

- Slow down -Shorter in wavelength -Change direction

Bulb - When it lights, shows current is flowing                                                                              Fuse - Melts when current is greater than fuse's current rating                                                    Voltmeter - Measures size of potential difference                                                                     

Ammeter - Measures current                                                                                                        Light dependant resistor (LDR) - Low in bright light and higher when light intensity is low.          Thermistor - Changes with temperature. Resistance of thermister is low at high temp and high at low temp.                                                                                                                                 

Variable resister- Allows current to be varieable                                                                        Resistor - Affects size of current                                                                                                    Diode- Only allows current to flow in 1 direction                                                                                 

Battery - Two or more cells in series                                                                                                Cell - Store chemical energy                                                                                                       

Switch closed - So current can flow                                                                                            Switch open - Reopens circuit, turning current off                                                                   

Series                                                                                                                                          When you close switch, flow of electrons around circuit. Flow of current. No branches so goes electrons go in 1 direction. Electrons give bulb energy. Measure current using ammeter (A).

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Parallel                                                                                                                                        Current flows through 2 branches. Current can be different on branches but total has to be same.

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The circuit flowing around circuit is calculated by:

Q = It      charge flow = Current     time The more charge flowing the higher the current.

If you measure current and potential difference through a resisor at a constant temperature, current and voltage are proportional.

Potential difference = Current  Resistance

V = I   R 

1) When potential difference across lamp is 3.3V the current ois 0.15 A Calcualte resistance?

3.3 divided by 0.15 = 22

- Voltage of uk electricity supply = 230V

-Frequency of uk electricity supply = 50Hz

Alternaitng current (AC), changes direction, plug socket  Direct current (DC), 1 direction, Batteries

Ocilloscope - Shows how current varies

Neutral wire - Blue                      Earth wire - Green/Yellow                          Live wire - Brown

Live wire is always carrying current.

Neutral wire carries current only when applaince is on.

Earth wire protects us from shocks as live wire has 230V so earth takes it down.

Resistance is measure of how hard it is fore current to flow through component. 

Resistance in wire is caused by electrons colliding with metal ions. The more collisons the higher the resistance the lower the current.     

Resistance of wire depends on temperature,material,length and thickness.

Material - Some materials are better conductor's than other's. Copper's ability to conduct electricity means often used in wiring.

Length - When length of wire is increased, electrons have to travel further, so chance of collisons increase so longer length of wire the higher resistance.

Temperature - Higher temperature, higher resistance. Metal ions vibrate more so more collions, so current lower.

Thickness - Thicker the wire, more space for electrons to flow so fewer collisions so resistance is lower and current is higher

Solid - Closely packed and regualr pattern. Low energy. Fixed position. Strong bonds and not easily compressed (Squeezed).

Liquid- Closely packed and free to move. More energy than solids. Takes shape of container and weaker forces of attraction.

Gas - Fills container. Easily compressed. Spread out and no pattern. Random direaction and has most energy.

- Energy stored by particles that make up a system ( Total kinetic and potential energy) 

Kinetic energy on:  -Speed -Mass

Ek =          mass      velocity

Heating increases temperature of kinetic energy

Heating increases change in state of potential energy.

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Potential energy incraeses as particles get apart.

When temp incraeses kinetic energy incraeses. Kinetic energy affected by temp of substance because as this increases velocity of particle increases.

- Tells us amount of energy needed to raise the temperature of 1kg of a substance by 1'c

Energy = Mass  change in temp   heat capacity        E = Mc    T

1) What is the energy required to heat 4kg of iron from 22'c to 50'c if C= 450/J/kg/'c

50 - 22 = 28' c         4kg  28  450 = 50400J

- Of a substance is amount of energy required to change the state of 1kg of a pure substance without change in temperature

E = mc    

Specific latent heat of fusion = Solid to liquid. 1kg of solid into 1kg of liquid at constant temperature

Specific latent heat of vaperation = Energy needed to change 1kg of liquid into 1kg of gas at constant temperature

1) 987 800 J is supplied to turn 2.2kg of liquid into gas.

987 800    2.2kg = 449000

2) 183 600J is supplied to turn 3.4kg of solid into liquid.

183600J    3.4kg = 54000 J/kg

Pressure depends on: -Force -Area      

How could we increase pressure in a gas?

- Increase number of particles - Decrease volume   - Increase temperature so particle moving faster so collide with each other with more energy    -Increase mass of particles

Increasing pressure

Particle with graeter mass ------------------>greater force of collision ----------------> Greater pressure

High temp-------->Particles move faster-------->Greater number of collision-------->Greater pressure

Greater number of particles-----------------> More collision -----------------> Greater pressure

Smaller volume----->Same number of particles but smaller area--------->More collisions per second------------> Greater pressure

Resultant force is overall force.

R.F= 10-8=2N  

If forces on an object are balanced, then no resultant force.

If object is stationary, will remain stationary.

If object is moving, continues to move at same speed and direction.

If forces on an object are unbalanced, then resultant force.

The object may accelerate or deaccelerate in direaction of resultant force.

Object may change direction.

Speed = 

1) Laura covers 200m in 1000 seconds. What is her speed?

200 divided by 100 = 2 m/s 

Constant speed forwards..No movement..Getting faster..Getting slower.Constant speed backwards

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Slowest line is shallow

Fastest line is steep

Accelerartion = 

1) A car accelerates from rest up to a speed of 30 m/s in 12 seconds. Calcualte acceleration.

30 m/s  divided by 12 seconds = 2.5 m/s 

Velocity time graphs

Gradient of velocity time graph gives acceleration

No movement..Constant speed..Constant acceleration..Constant deacceleration..

---> Falling objects in water or air reach a top speed called terminal energy

---> As you move faster and faster the air resistance increases because you have to push more air particles out of the way each second.

--->Eventually air resistance increases until it equals the weight of falling objects

Skydiver                                                                                                                                            1) At the start of his jump the air resistance is small so he accelerates downwards.

2) As his speed increases his air resistance will increase.

3) Eventually air resistance will be large enough to balance the skydiver's weight. At this point the forces are balacned so his speed becomes constant.

4) When he opens his parachute the air resistant increases, causing him to start deacelerating.

5) Because he is slowing down his air resistance will decrease again until it balances his weight. The skydiver has now reached a new lower terminal velocity.