physics

Energy stores

a system is an object or group of objects, when a system changes, the way energy is stored also changes

examples of energy stores

vehicle slowing down, system is vehicle moving and when it slows down, the kinetic energy transfers to thermal due to friction between the wheels and brakes

how to calculate kinetic energy

E = ½ x mv²

E = joules

mass = kg

v = speed in m/s

How to calculate elastic potential

E = ½ x ke²

E = joules

k = spring constant in N/m

e = extension in m

How to calculate Gravitational Potential Energy

E = mgh

E = joules

m = mass in kg

g = gravitational field strength in N/kg (9.8)

h = height in meters

How to calculate specific heat capacity

the energy required to raise the temperature of 1kg of a substance by 1 degrees or 1K

Energy = mass x specific heat capacity x temperature change

E = mcΔT
E = joules
m = mass in kg
c = specific heat capacity in J/(kg·K)
ΔT = change in temperature in K

How to calculate power

power = energy transferred/time = work done/time

P = E/t = W/t

power = watts (W)

energy = joules J

time = seconds

work done = joules J

why can one motor do the same work but faster

energy is transferred at a faster rate

Energy transfers

energy can be transferred, stored or dissipated but cannot be created or destroyed. Energy is usually called wasted when dissipated

how to reduce energy waste

Lubrication:

• oil in a motor

• reduces friction

• so less energy is lost (as heat) through frction

Thermal insulation:

• double glazing

• less useful thermal energy is lost

thermal conductivity

The higher the thermal conductivity of a material, heat is allowed to travel through the material more easily, so the higher the rate of energy transfer by conduction across the material

thermal conductivity in a building

rate of cooling is low if walls are thickk and thermal conductivity walls are low. if the walls are thin metal sheets, heat would be lost very quickly

efficiency

ratio of useful work done by machine, engine, device to the energy supplied to it, which is often expressed as a percentage

efficiency = useful energy output/ total energy input = useful power output/total power input

how can efficiency be increased

• reducing waste output (lubrication, thermal insulation)

• reducing waste output (absorbing thermal waste and recycling as input energy)

non renewable energy sources

• fossil fuels (coal, oil, gas)

• nuclear fuel

renewable energy resources

• biofuel

• wind

• hydro-electricity

• geothermal

• tidal

• solar

• water waves

renewable and non-renewable energy

• renewable energy can be replenished (wind will never stop)

• non - renewable is used for large scale energy

• renewable resources cannot provide such a large amount of energy so easily

• renewable energy has become more important due to the finite lifetime of fossil fuels and so their development has become more important

• renewable energy is not always most reliable:

  solar doesnt work in bad weather

  wind is only intermittent

main energy uses

• transport

• electricity generation

• heating

environmental impact

• extraction of energy:

  fossil fuels involve destroying landscapes

  wind turbines can be considered an eyesore

• useful energy sources

  fossil fuels release harmful emissions

  solar, wind directly create electricity with no emissions

patterns an trends of energy use

During industrial revolution, fossil fuels became an important source of energy as it was easy to mine, and provided a lot of energy

- Only recently has renewable energy become more suitable

– technology has had to develop a lot since industrial revolution to be able to harness such energy sources efficiently

- It is easier to use energy resources due to increasing pressure to cope with the public’s increasing power demands but harder to solve environmental issues due to political, social, ethical and economic considerations.

What is electricity?

The movement of charged particles (ions) in a wire.

What is electrolysis?

Using electricity to split something up

What is Potential difference measured in?

Volts (V)

Symbol for variable resistor

symbol for switch

Symbol for cell

Symbol for battery

symbol for lamp

symbol for voltmeter

Symbol for ammeter

symbol for motor

symbol for resistor

symbol for diode

symbol for light emitting diode (LED)

symbol for fuse

symbol for light dependent resistor (LDR)

What is a switch?

it opens and closes a circuit

What is a lamp?

it transfers electrical energy to light energy

What is a voltmeter?

it measures the potential difference using volts

What is a ammeter?

it measures the flow of current

What is a resistor?

it limits the amount of current passing through

What is a variable resistor?

it controls the amount of current passing through

What is a motor?

it changes electricity to mechanical energy

What is a diode?

it only allows current to flow one way

What is a light emitting diode (LED)?

a diode that emits light when current passes through

What is a fuse?

it only allows certain amounts of current until it melts

What is a thermistor?

it changes resistance by the temperature changing

what is a Light dependent resistor (LDR)?

a resistor which changes amount of current passing through by the amount of light

What is electron flow?

electrons negatively charged repelling against negative battery or cell

What is Alternating current (AC)?

current oscillates direction at a certain frequency

What is Direct current (DC)?

voltage is constant

What is the UK power outlet frequency (cycles per second)?

50 cycles per second (hertz

What is the cycles that AC oscillates measured in?

Cycles per second or Hertz (Hz)

What is current?

the flow of charged particles

What is charge measured in?

Coloumbs (C)

What is the formula for charge?

Charge= time x current

Q=I x t

What is the formula for resistance?

resistance= potential difference (Voltage) / current

R= V/I

What are the parts in a electric generator?

fuel system, Engine, alternator, voltage regulators, cooling and exhaust systems, lubrication system, battery, frame, control panel, enclosure

How is electricity generate in a generator?

A magnet moves in and out of a coil, generating a magnetic field opposing the motion. An alternating current and voltage is generated.

What are factors effecting resistance?

Material of wire, length of wire, thickness of wire, temperature, changing voltage, changing resistance

What is resistance?

when electrons collide with ions, preventing them from flowing through

How does temperature affect resistance?

When temperature increases, resistance increases as well because electrons have more energy in them and move around more randomly. his means they are more likely to hit other ions and therefore create more resistance.

How does the length of wire affect resistance?

the longer thew wire, the greater the resistance

How does resistance vary with a diode?

the diode only lets current flow in one direction except for at large negative breakdown voltages

How does resistance vary with a LDR?

resistance increased when there was no light. This is because when light shines on it, it releases electrons which increase the amount of electrons to carry the current. therefore when the light increases, the current also increases, resulting in a reduction of resistance.

How does resistance vary with a filament lamp?

resistance of a filament lamp increases as the tempreature of the dilament lamp increases. reversing the voltage reverses the ditrrection of the electivc current but doen't change the shape of the curve. The lamp doesn't obey Ohm's law.

How does resistance vary with a thermistor?

As the current increases the thermistor gets hotter, releasing more electrons, resulting in a reduction in resistance. This is because the the thermistor is a semiconductor and conducts electricity when heated. The thermistor doesn't obey Ohm's law

What is Ohm's law?

The voltage and the current are directly propotional.

what does a direct current graph line look like?

horizontal line above 0 for current with no changes over time.

What does a alternating current graph look like?

Alternating current has dips to 0 for the current as it oscillates in a set time.

What is current measured in?

Amperes (amps)

What is the national grid?

the electricity going from the power station at 25KV to a step-up transformer which increases the potential difference to 132KV in power lines which reach step down transformers. Electricity then reaches factories which use it and dispose of excess by sending to homes at 230V

what is the generator effect?

When the wire stops moving, the potential difference disappears, the direction of the potential difference swaps each tome we change the direction, wire is experiencing a change in the magnetic field., the wire has to be touching the magnetic field.

How to change the size of the included potential difference?

change the magnetic field- stronger magnets, more wire or magnets, quicker- the faster the magnetic field would changer, shape he wire like a coil- more turns

What is an electromagnet?

using electricity to create a magnet

How do transformers work?

alternating potential difference causes a current to flow (will also alternate). A magnetic field around the coil induces an alternating magnetic field in the iron core, induces a potential difference, causing a current to flow if part of a complete circuit.

What are components in a transformer?

a primary coil- draws from the power source, secondary coil- changes the voltage, iron core- converts low voltage into high. voltage or vice-versa.

What does a step up transformer have?

primary coil has less turns than secondary coil

What does a step down transformer have?

primary coil has more turns than secondary coil.

What is the equation for transformer ratios and number of coils?

Vp/Vs = Np/Ns

V= voltage or potential difference

N= number of coils

p= primary coils

s= secondary coils

What is the equation for transformer ratios and current?

Vp x Ip = Vs/Is

V= voltage or potential difference

I= current

p= primary coils

s= secondary coils

what is the equation for power in electricity using voltage and current?

power= current x voltage

p=IV

What is power?

the amount of energy transferred in a second

what is power measured in?

J/s or Watts

what is the equation for power in electricity using current and resistance?

Power = current sq x resistance

P= IxIxR

What is the equation for potential difference using energy and charge?

potential difference = energy/charge

V= E/Q