combined physics ht paper 1

Energy is transferred between stores

Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, nuclear

Energy is transferred...

Mechanically (by a force doing work), electrically (work done by moving charges), by heating or by radiation (like light or sound)

When a system changes, energy is transferred

It can be transferred into or away from the system, between objects in the system or between different types of energy stores. Closed systems are where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always 0

kinetic energy

energy of motion - the greater an object's mass and the faster it is going, the more energy there will be in its kinetic energy store. Ek (j) \= 1/2m(kg)v(m/s) squared

Raised objects store energy in gravitational potential energy stores

lifting an object in a gravitational field requires work, causing an energy transfer to the the GPE store of the object. Ep(j) \= m(kg)g(n/kg)h(m)

Falling objects transfer energy

Falling objects transfer energy from its GPE store to its kinetic energy store. When there's no air resistance, energy lost from the GPE store \= energy gained in the kinetic energy store

Stretching transfers energy to elastic potential energy stores

As long as the limit of proportionality has not been exceeded, Ee (j) \= 1/2 k (N/m) e (m) squared

specific heat capacity

the energy required to raise the temperature of one gram of a substance by one degree Celsius. 🔼E (j) \= m(kg) c(j/kgdegree) 🔼theta (degrees Celsius)

Conservation of energy principle

Energy can be transferred but can never be created of destroyed

Dissipated energy

energy used up in a system, typically lost due to work done by friction, 'wasted energy'

Phone energy

When you use the phone, energy is usefully transferred from the chemical energy store of the battery in the phone, but some of this energy is dissipated to thermal energy

Closed system energy transfer

A cold spoon is dropped into hot soup in an insulated flask, which is then sealed. Energy is transferred from the thermal energy store of the soup to the useless thermal energy of the spoon

Power

The rate at which work is done (watts). P(w) \= E(j) / t(s)

Powerful machine

One which transfers a lot of energy in a short space of time

Conduction occurs mainly in solids

Conduction is the process where vibrating particles transfer energy to neighbouring particles.

Long definition of conduction

Energy transferred to an object by heating is transferred to the thermal store, which is shared across the kinetic store of the particles. The particles' collisions cause energy to be transferred between particles kinetic energy stores.

thermal conductivity

the Mrs sure of the rate at which thermal energy can travel through a material

Convection occurs only in liquids and gases

Convection is where energetic particles move away from hotter to cooler regions

Convection longer definition

Unlike in solids, the particles in liquids and gases are able to move. When you heat a region of a gas/liquid, the particles move faster and the space between particles increases. This causes the density of the region to decrease. Because they can flow, the warmer and less dense region will rise above denser cooler regions. If there is a constant heat source, a convection current will be made

Radiators - convection currents

Energy is transferred from the radiator to nearby air particles by conduction. The air by the radiator becomes warmer and less dense. This warm air rises and is replaced by cooler air. At the same time, the previously heated air transfers energy to the surrounding and cools, becomes denser, and sinks. This cycle repeats and causes a flow of air to circulate around the room

How to reduce unwanted energy transfers

Lubrication and thermal insulation

Lubrication reduces frictional forces

When something moves, there's at least one frictional force acting on it, causing some energy to be dissipated. For objects that are rubbed together, lubricants reduce the fiction between the object's surfaces when moved. Lubricants tend to be liquids (like oil) to flow easily between objects and coat them

Insulation reduces the rate of energy transfer by heating

Things to do to prevent energy loss through heating...

\-have think walls made from low thermal conductivity material. This makes the rate of energy transfer slower, so the building will cool more slowly.

\-use thermal insulation

Thermal insulation examples

* cavity walls made of an inner and outer wall with an air gap in between to reduce the amount of energy transferred by conduction.
* loft insulation can reduce convection currents created in lofts
* double glazed windows have an air gap between two layers of glass to prevent energy transfer by conduction
* draught excluders around doors and windows reduce energy transfers by convection

Most energy transfers involve some waste energy

Efficiency \= useful output energy transfer / total input energy transfer OR efficiency \= useful power output / total power input

Non renewable energy resources will one day run out

Fossil fuels and nuclear fuels. Fossil fuels are typically burnt to provide coal, oil, and natural gas. They damage the environment but provide most of our energy

Renewable energy resources will never run out

These are: the sun, wind, water waves, hydro-electricity, bio-fuel, tides, geothermal. Most of them do damage to the environment, but in less nasty ways than non renewables. However, they don't provide much energy and some are unreliable as they depend on the weather

Energy resources can be used for transport

Non renewable - petrol and diesel powered vehicles use fuel from oil. Coal can be used in old fashioned steam trains to boil water for steam.

Renewable - vehicles running on bio-fuels or a mix of a bio-fuel and petrol/diesel.

Electricity sometimes powers vehicles and can be generated using renewable or non renewable resources

Energy resources can also be used for heating

Non renewable - natural gas is widely used for heating homes. The gas heats water, which gets pumped into radiators. Coal is commonly burnt in fireplaces. Electric heaters use electricity generated from non renewable resources.

Renewable - a geothermal heat pump uses geothermal energy resources to heat buildings. Solar water heaters use to the sun to heat water, which gets pumped into radiators.

Wind power

This involves putting up lots of wind turbines in an exposed place, like on coasts. The turbines have a generator inside them - the rotating blades turn the generator to produce electricity.

wind power advantages

There's limited pollution (only when they're first manufactured), no fuel costs and minimal running costs, no permanent damage to the landscape

wind power disadvantages

They spoil the view, very noisy, unreliable as they depend on the weather, initial costs are quite high

Solar cells

They generate electric currents from the sun. They are often the best energy source to charge calculator or watch batteries, as they don't use much electricity.

solar power advantages

There's no pollution (although they use a lot of energy to manufacture), reliable in sunny countries in the daytime, energy is free and running cost extremely low

solar power disadvantages

Unreliable because they depend on weather, can't increase power output when there is extra demand, initial costs are high school

Geothermal power

This is energy in underground thermal energy stores. It is possible in volcanic areas or where hot rocks lie close to the surface. The source of a lot of this energy is the slow decay of various radioactive elements deep inside the earth

Geothermal power advantages

Free energy that is reliable and does very little damage to the environment. Can be used to generate electricity or heat buildings

Geothermal power disadvantages

There aren't many suitable locations for power plants, and the cost of building a power plant is high compared to the amount of energy that it produces

hydroelectric power used falling water

It tends to require the flooding of a valley by building a dam. Water is allowed out through turbines

Hydro-electric power advantages

There is no pollution and it can provide an immediate response to an increased demand for electricity. It is reliable and there are no fuel costs and minimal running costs

Hydro-electric power disadvantages

There is a big environmental impact from the valley flooding (rotting vegetation releases methane and CO2) and loss of habitat for some species. Initial costs are high

Water power

Lots of small wave-powered turbines around the coast. The moving turbines are connected to a generator

Water power advantages

There is no pollution, no fuel costs and minimal running costs. Can be useful on small islands

Water power disadvantages

It disturbs the seabed and the marine animals' haibitats. Spoils the view, hazard to boats, fairly unreliable, initial costs are high

Tidal barrages

Tidal barrages are big dams across river estuaries, with turbines in them. As the tide comes in the estuary gets filled up. The water is then allowed out through turbines at a controlled speed. Tides are produced by the gravitational pull of the moon and sun

Tidal barrages advantages

There is no pollution, pretty reliable as they always happen twice a day, no fuel floats and minimal running costs

Tidal barrages disadvantages

It prevents free access for boats. Spoils the view, and alters habitat, the height of the tide is variable, initial costs are moderately high

Bio-fuels

These are renewable energy resources created from plant products or animal dung. They can be solid, liquid, or gas and can be burnt to produce electricity or run cars in a similar way to fossil fuels

Biofuel advantages

They are fairly reliable as crops take a relatively short time to grow and some crops can grow all year round.

Biofuel disadvantages

They can't respond to immediate energy demands - to combat this, biofuels are continuously produces and stored. The cost to refine them is very high. Sometimes large areas of forest have been cleared for room to grow bio-fuels, resulting in species losing their natural habitats. The decay and burning of this vegetation increases CO2 and Meghan emissions

Non-renewable resources are reliable

There is enough fossil and nuclear fuels to meet current demand, and are extracted from the earth fast enough that power plants always have fuel, meaning they can respond quickly to demand. However, they are slowly running out. While the set up costs of power plants is high, the running costs aren't expensive.

nonrenewable resources create environmental problems

Coal, oil, and gas release CO2 when burned which adds to the greenhouse effect and contributes to global warming. Burning coal and oil release sulfur dioxide, leading to acid rain. Power plants spoil view. Oil spillage cause serious environmental problems, affecting animals.

Currently we still depend on fossil fuels

In the 20th century, The electricity use of the uk massively increased as the population grew. Since the start of the 21st century, it is slowly decreasing as we get better at being more efficient and careful. Most of our electricity is produced using fossil fuels. We are trying to increase our use of renewable energy resources. This move to renewable energy has been triggered by...

People want to use more renewable energy resources

We went to do less harm to the environment as we are aware of the consequences. We are aware non renewables will one day run out. Car companies have been affected by this change in attitude. Electric cared and hybrids are already being sold and their popularity is growing

The use of renewables is limited by reliability, money, and politics

Although scientists can advise, they don't have the power to make people change their behaviour. Building renewable power plants is expensive and so some energy providers are reluctant to do this. They might not be reliable , meaning more research would have to be done. Making personal changes can be expensive - hybrid cars are expensive as are solar panels

Charge flow \=

Current x time

What is current

The flow of electric charge (amps)

What is resistance

Any thing that slows the flow down

What is pd (or voltage)

The driving force behind the charge

Potential difference \=

Current x resistance

What measures current

An ammeter put in series

What measures pd

A voltmeter put in parralell

What does an ohmic conductor have

What does a phillament lamp IV characteristic graph look like

What does a diode IV characteristic graph look like

When is resistance highest in LDRs

Dark places

When is resistance highest in Thermistors

In cold

What happens to potential difference in a series circuit

Is is shared

V=v1+v2 etc

What happens to current in a series circuit

It is the same

What happens to resistance in a series circuit

Resistance adds up

What happens to potential difference in parallel circuits

It is the same

What happens to current in a parralell circuit

It is shared

What happens to resistors in a parralell circuit

It reduces the total resistance

total resistance of 2 resistors is less than the smallest individual resistor

What is mains supply

Ac (p+n ends alternate) 230v, 50hz

What is the blue wire

Neutral

What is the red wire

Live, provides ac

What is the green and yellow wire

Earth wire

When charge flows in a circuit...

... work is done

National grid uses

High PD low current so less energy lost to surroundings. This is charged by step up and step down transformers

What is the national grid

System of cables and transformers that cover the uk and connects power stations to consumers

What is battery supply

Dc

Build up of static is caused by

Friction, negative electrons are scraped off

What does too much static cause

Sparks.

High PD -> strong electrical field -> electrons to be removed -> current flows through air -> spark

Electric field lines go

From positive to negative

Charged objects in an electric field

Feel a force

What does a diode look like?

What does a resistor look like?

What does a variable resistor look like?

What does a LED look like?

What does a fuse look like?

What does a thermistor look like?

What does a LDR look like?

for a circuit to work....

it must have a source of potential difference

How do objects become charged with static electricity?

when certain insulating materials are rubbed against each other, - particles move from one to the other.

How does sparking happen?

electrical charge builds on the object and if the PD is large enough(large PD, strong electric field) , electrons jump across, this is a spark.

What happens to like and opposite charges?

like charges repel, opposites attract

Explain the concept of an electric field?

a charged object creates an electrical field around itself. the electric field is strongest close to the charged object.

What does the electric field of a + and - particle look like

when a second item is added in the field...

it feels a force (attraction or repulsion) the further away, the weaker the force.

define density

it is a mass of an object per unit volume