Physics paper 1

Energy can be stored in a variety of different energy stores.

Energy is transferred by heating, by waves, by an electric current, or by a force when it moves an object.

When an object falls and gains speed, its store of gravitational potential energy decreases and its kinetic energy store increases.

When a falling object hits the ground without bouncing back, its kinetic energy store decreases. Some or all of its energy is transferred to the surroundings - the thermal energy store of the surroundings increases, and energy is also transferred by sound waves.

Energy cannot be created or destroyed. Conservation of energy applies to all energy changes.

A closed system is a system in which no energy transfers take place out of or into the energy stores of the system.

Energy can be transferred between energy stores within a closed system. The total energy of the system is always the same, before and after, any such transfers.

Work is done on an object when a force makes the object move.

Energy transferred = work done. Work done is W = F x s where F is the force and s is the distance moved (along the line of action of the force).

Work done to overcome friction is transferred as energy to the thermal energy stores of the objects that rub together and to the surroundings. The gravitational potential energy store of an object increases when it moves up and decreases when it moves down.

The gravitational potential energy store of an object increases when it is lifted up because work is done on it to overcome the gravitational force.

The gravitational field strength at the surface of the moon is less than on the earth.

The change in the gravitational potential energy store (J) = mass (kg) x gravitational field strength (N/kg) x change of height (m).

Change in objects gravitational potential energy store (J) = weight (N) x change of height (m).

Work is done on an object when a force makes the object move.

Energy transferred = work done. Work done is W = F x s where F is the force and s is the distance moved (along the line of action of the force). Work done to overcome friction is transferred as energy to the thermal energy stores of the objects that rub together and to the surroundings.

The gravitational potential energy store of an object increases when it moves up and decreases when it moves down.

The gravitational potential energy store of an object increases when it is lifted up because work is done on it to overcome the gravitational force.

The gravitational field strength at the surface of the moon is less than on the earth.

The change in the gravitational potential energy store (J) = mass (kg) x gravitational field strength (N/kg) x change of height (m).

Change in objects gravitational potential energy store (J) = weight (N) x change of height (m).

The energy in the kinetic energy store of a moving object depends on its mass and its speed.

The kinetic energy store of an object is: KE (J) = ½ x mass (kg) x speed² (m/s)²

Elastic potential energy is the energy stored in an elastic object when work s done on the object.

The elastic potential energy stores in a stretched spring is: EPE (J) = ½ x spring constant (N/m) x extension² (m)²

Useful energy is energy in the place we want it and in the form we need it.

Wasted energy is the energy that is not useful energy and is transferred by an undesired pathway.

Wasted energy is eventually transferred to the surroundings, which become warmer. As energy dissipates (spreads out), it gets less and less useful.

The efficiency of a device = useful energy transferred by the device ➗ total energy supplied to the device (x100%). No energy transfer can be more than 100% efficient.

Machines waste energy because of friction between their moving parts, air resistance, electrical resistance, and noise,

Machines can be made more efficient by reducing the energy they waste. For example, lubrication is used to reduce friction between moving parts.

Electricity and gas and/or oil supply most of the energy you use in your home. Electrical appliances can transfer energy in the form of useful energy at te flick of a switch.

Uses of everyday electrical appliances include heating, lighting, making objects move (using an electric motor), and producing sound and visual images.

An electrical appliances is designed for a particular purpose and should waste as little energy as possible.

The more powerful an appliance is, the faster the rate at which it transfers energy.

Power is rate of transfer of energy.

The power of an appliance is: power = energy transferred to appliance (J) / time taken for energy to be transferred (s)

Efficiency of a device is useful power out ➗ total power in (x 100%)

Power wasted by an appliance = total power input - useful power out.

Metals are the best conductors of energy.

Non- metals materials such as wool and fibreglass are the best insulators.

The higher the thermal conductivity of a material, the higher the rate of energy transfer through it.

The thicker a layer of insulating material, the lower the rate of energy transfer through it.

All objects emit and absorb infrared radiation. The hotter an object is, the more infrared radiation it emits in a given time.

Blackbody radiation is radiation emitted by a body that absorbs all the radiation incident on it.

The temperature of an object increases if it absorbs more radiation than it emits.

The Earth’s temperature depends on a lot of factors, including the absorption of infrared radiation from the sun, and the emission of radiation from the Earth’s surface and atmosphere.

The specific heat capacity of a substance is the energy needed to raise the temperature of 1 kg of the substance by 1℃.

Energy transferred,△E (J) = mass,m (kg) x specific heat capacity (J/kg℃) x temperature change,△θ (℃)

The greater the mass of an object, the more slowly its temperature increases when it is heated.

To find the specific heat capacity, c of a substance, use a joulemeter and a thermometer to measure △E and △θ for a measured mass m, then use c = △E/ m x △θ

Electric and/or gas heaters and gas or oil- fired central heating or solid- fuel stoves are used to heat houses.

The rate of energy transfer from houses can be reduced by using:

• Loft insulation

• Cavity wall insulation

• Double- glazed windows

• Aluminium foil behind radiators

• External walls with thicker bricks and lower thermal conductivity.

Cavity wall insulation is insulation material that is used to fill the cavity between the two brick layers of an external house wall.

Electric and/or gas heaters and gas or oil- fired central heating or solid- fuel stoves are used to heat houses.

The rate of energy transfer from houses can be reduced by using:

• Loft insulation

• Cavity wall insulation

• Double- glazed windows

• Aluminium foil behind radiators

• External walls with thicker bricks and lower thermal conductivity.

Cavity wall insulation is insulation material that is used to fill the cavity between the two brick layers of an external house wall.

Your energy demands are met mostly by burning oil, coal and gas.

Nuclear power, biofuels, and renewable resources provide energy to generate some of the energy you use.

Uranium or plutonium is used as the fuel in a nuclear power station. Much more energy is released per kilogram from uranium or plutonium than from fossil fuels.

Biofuels are renewable sources of energy. Biofuels such as methane and ethanol can be used to generate electricity.

A wind turbine is an electricity generator on top of a tall tower. 

Waves generate electricity by turning a floating generator.

Hydroelectricity generators are turned by water running downhill.

A tidal power station traps each high tide and uses it to turn generators.

Solar cells are flat solid cells and use the Sun’s energy to generate electricity directly. Solar heating panels use the Sun’s energy to heat water directly.

Geothermal energy comes from the energy transferred by radioactive substances deep inside the earth. 

Water pumped into hot rocks underground produces steam to drive turbines at the earth’s surface that generate electricity.

Fossil fuels produce increased levels of greenhouse gases, which could cause global warming. Nuclear fuels produce radioactive waste.

Renewable energy resources will never run out, they don’t produce harmful waste products (eg. greenhouse gases or radioactive waste), and they can be used in remote places. But they cover large areas, and they can disturb natural habitats.

Different energy resources can be evaluated in terms of reliability, environmental effects, pollution and waste.

Gas- fired power stations and pumped- storage stations can meet variations in demand.

Nuclear power stations are expensive to build, run, and decomposition. Carbon capture of fossil fuel emissions is likely to be very expensive. Renewable resources are cheap to run but expensive to install.

Nuclear power stations, fossil- fuel power stations that use carbon capture technology, and renewable energy resources are all likely to be needed for future energy supplies.

Some insulating materials become charged when rubbed together.

Electrons are transferred when objects become charged:

• Insulating materials that become positively charged when rubbed lose electrons.

• Insulating materials that become negatively charged when rubbed gain electrons.

Like charges repel. Unlike charges attract.

The force between two charged objects is a non- contact force.

Every component has its own agreed symbol. A circuit diagram shows how components are connected. A battery consists of two or more cells connected together. 

Thes size of an electric current is the rate of flow of charge.

The equation for the electric current of a circuit is I = Q/t. This equation can be rearranged to find charge flow or time: Q = I x t or t = Q/I

Potential difference across a component, V = energy transferred, E / charge, Q.

Resistance, R = potential difference, V / current, I.

Ohm’s law states that the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor.

Reversing the potential difference across a resistor reverses the current through it.

The resistance of an appliance is R = V / I

A filament lamp resistance increases if the filament temperature increases.

Diode: forward resistance low; reverse resistance high.

A thermistor’s resistance decreases if its temperature increases.

An LDR’s resistance decreases if the light intensity on it increases.

For components in series:

• The current is the same in each component

• The total potential difference is shared between the components

• Adding their resistances gives the total resistance

For cells in series, acting in the same direction, the total potential difference is the sum of their individual potential differences.

Total resistance = resistor 1 + resistor 2

Adding more resistors in series increases the total resistance because the current through the resistors is reduced and the total potential difference across them is unchanged.

For components in parallel:

• The total current is the sum of the currents through the separate components

• The potential difference across each component is the same.

The bigger the resistance of a component, the smaller the current that will pass through that component.

The current through a resistor in a parallel circuit is I = V / R

Adding more resistors in parallel decreases the total resistance because the total current through the resistors in increased and the total potential difference across them is unchanged.

Direct current (d.c) flows in one direction only. Alternating current (a.c) repeatedly reverses its direction of flow. A mains circuit has a live wire, which is alternatively positive and negative every cycle, and a neutral wire at zero volts.

The peak potential difference of an a.c. supply is the maximum voltage measured from zero volts. To measure the frequency of an a.c. supply, measure the time period of the waves, then use the equation; frequency = 1 ➗ time taken for 1 cycle.

Sockets and plug cases are made of stiff plastic materials that enclose the electrical connections. Plastic is used because it is a good electrical insulator.

A mains cable is made up of two or three insulated copper wires surrounded by an outer layer of flexible plastic material. In a three pin plug or a three- core cable, the live wire is brown, the neutral wire is blue and the earth wire is striped green and yellow.

The earth wire is connected to the longest pin in a play and is used to earth the metal case of a mains appliance.

The power supplied to a device is the energy transferred to it each second. The energy transferred to a device is E = P x t. The electrical power supplied to an appliance is equal to P = I x V. The correct rating (A) for a fuse = electrical power (watts) ➗ potential difference (volts).

The charge flow is Q = I x t.

When charge flows through a resistor, energy transferred to the resistor makes it hot.

The energy transferred to a component is E = V x Q.

When charge flows around a circuit for a given time, the energy supplied by the battery is equal to the energy supplied by the battery is equal to the energy transferred to all the components in the circuit.

A domestic electricity meter measures how much energy is supplied. The energy supplied to an appliance is E = P t. Useful energy used = efficiency x energy supplied.

Density = mass ➗ volume (in kg/m3)

To measure the density of a solid object or a liquid, measure it’s mass and its volume then use the density equation p = m ➗ v

Rearranging the density equation gives m = pv or v = m➗ p

Objects that have a lower density than water float in water. The density of a substance is defined as its mass per unit volume. The particles of a solid are held next to each other in fixed positions. They are the least energetic of the states of matter.

The particles of a liquid move about at random and are in contact with each other. They are more energetic than particles in a solid.

The particles of a gas move about randomly and are far apart (so gases are much less dense than solids and liquids). They are the most energetic of the states of matter.

When a substance changes state, it’s mass stays the same because the number of particles stays the same.

For a pure substance:

• Its melting point is the temperature at which it melts (which is the same temperature at which it solidifies)

• It’s boiling point is the temperature at which it boils (which is the same temperature at which it condenses).

Energy is needed to melt a solid or to boil a liquid.

Boiling occurs throughout a liquid at its boiling point. Evaporation occurs from the surface of a liquid when its temperature is below its boiling point.

The flat section of a temperature - time graph gives the melting point or the boiling point  of a substance.

Increasing the temperature of a substance increases its internal energy. The strength of the forces of attraction between the particles of a substance explains why it is a solid, a liquid, or a gas.

When a substance is heated:

• If its temperature rises, the kinetic energy of its particles increases

• if it melts or it boils, the potential energy of its particles increases.

The pressure of a gas on a surface is caused by the particles of the gas repeatedly hitting the surface. Latent heat is the energy needed to for a substance to change its state without changing its temperature.

Specific latent heat of fusion (or of vaporization) is the energy needed to melt (or to boil) 1kg of a substance without changing its temperature. In latent heat calculations, use the equation E = mL. The specific latent heat of ice (or of water) can be measure using a low voltage heater to melt the ice (or to boil the water).

The pressure of a gas is caused by the random impacts of gas molecules on surfaces that are in contact with the gas. 

If the temperature of a gas in a sealed container is increased, the pressure of the gas increases because:

• The molecules move faster so they hit the surface with more force.

• The number of impacts per second of gas molecules on the surfaces of a sealed container increases, so the total force of the impacts increases.

The unpredictable motion of smoke particles is evidence of the random movement of gas Molecules.

For a fixed mass of gas at constant temperature:

• Its pressure is increased if its volume is decreased

• Reducing the volume of a gas increases the number of molecular impacts per second on the surfaces that are in contact with the gas.

Use the equation pressure x Volume  = constant if the mass and the temperature of the gas do not change.

The temperature of a gas can increase if it is compressed rapidly because work is done on it and the energy isn’t transferred quickly enough to its surroundings.