Paper 1 Physics

Voltage

The amount of work to be done to move a charge from one point to another along an electric circuit.

What is work done?

energy transferred

current

A flow of electric charge.

LDR

streetlights / light intensity decreases, resistance increases

Resistance

A material's opposition to the flow of electric current.

Current PD graph for a diode

Fuse function

To stop the current from flowing and avoid damage caused by heat or fire

step-up transformer

increases voltage and decreases current

step-down transformer

decreases voltage and increases current

Brown wire

live wire / right

Blue wire

neutral wire / left

Yellow/green wire

Earth wire / top

What does an earth wire do?

If a fault develops where the live wire touches the metal case, because it is earthed the electricity will escape the appliance through the wire.

What does the neutral wire do?

Completes the circuit and carries away current

Light Emmiting Diode (LED)

A type of diode that emits light when it conducts electricity

Diode

Allows current to flow in only one direction

alternating current

A flow of electric charge that regularly reverses its direction.

Direct Current (DC)

Electric current that flows in only one direction

static electricity

rubbing balloon w cloth invisible negative electrons build on balloon surface / electrons can pull light objects eg hair

Thermistor

Resistor which varies with temperature / fire alarm

LDR graph

As light intensity increases, resistance decreases

diode graph

current only flows in one direction / line at x then str8 up

series circuit

Current stays same / voltage is split

parallel circuit

Voltage stays same / current is split

Ohm's Law

Voltage is directly proportionate to current

lamp graph

curve left, str8, curve right

Resistor at constant temperature graph

Str8 like through origin

How do we get electric shocks

Difference in PD at 2 points

Plug in design

plastic insulator casing / copper cables conduct + malleable / fuse melts if C is too high

Why do appliances with plastic cases not need to be earthed?

Double insulated / live wire can't touch case

Compact Fluorescent Lamp (CFL)

A small fluorescent lamp / efficient alternative to filament bulb

Why is the live wire dangerous?

our bodies are at 0 V. If you were to touch a live wire, a big potential difference will act across your body, causing a current to flow through you. this causes a large electric shock which could injure or even kill you.

How is energy transferred?

Mechanically, electrically, heating, radiation

Chemical energy stores

includes fuels, food and the chemicals in batteries / transferred during chemical reactions

Kinetic energy stores

Describes the energy an object has because it is moving

Gravitational potential energy stores

the energy stored in an object because of its position / eg an object above ground

Elastic potential energy store

Energy stored in stretched or squashed things

thermal energy stores

the energy a substance has because of its temperature

What happens when an object falls

It gains speed and it's store of gravitational potential energy decreases, and kinetic energy store increases

What happens when a falling object hits the ground

Kinetic energy store decreases / most energy is transferred to surroundings - surrounding thermal energy store increases and energy transfers to sound waves

What is a closed system?

When no external forces act / no energy transfers take place

What is the conservation of energy?

Energy cannot be created or destroyed, only transferred

Equation for work done

Work done (j) = force (n) x distance (m)

What does the term work done mean

When a force makes the object move

What happens when work is done to overcome friction

Energy is transferred to thermal energy stores of the objects that rub together + surroundings

Describe how Gravitational potential energy changes as you go up / down

Increases when up / decreases when down

Why does gravitational potential energy increase when you lift objects up

Work is done to overcome gravitational force

What is the gravitational field strength of the earth

9.8 N / kg

How do you calculate the change of gravitational potential energy store

Mass (kg) x gravitational field strength (9.8) x change of height (m)

How do you calculate kinetic energy

1/2 x mass x velocity squared

How do you calculate elastic potential energy

1/2 x spring constant x extension squared

What is useful energy?

Energy transferred to where it is wanted in the way it is wanted

What is wasted energy?

Energy that is not usefully transferred (friction) / ends up transferred

How do you calculate efficiency

(Useful energy output / total energy input) x 100

How can machines be made more efficient

add lubricant

- reduces friction

How do machines waste energy

friction between their moving parts, air resistance, electrical resistance and noise

How do you calculate power

work/time = power (watts)

What is power?

the rate at which energy is transferred or work is done

How can you find the power wasted by an appliance

Total power input / useful power output

what is a radioactive substance

A substance that gives out radiation from the nuclei

what types of radiation come from radioactive substances

alpha, beta and gamma

what can you use to detect radioactivity

Geiger counter

How does a Geiger counter work?

It uses ions produced by radiation to create an electrical current.

how do you use a Geiger counter

the counter clicks every time radiation particles enter the tube

who discovered protons

Ernest Rutherford

Why are some substances radioactive?

They have an unstable nucleus and become stable by emitting radiation

What is radioactive decay?

spontaneous change in the nucleus of an atom

What did Rutherford discover?

That every atom has positive centre (nucleus) that contains most the mass

what is an isotope

atom of the same elements with different number of neutrons

What is a count rate

The number of decays recorded each second by a detector

What is a half life

It is the time for 1/2 a substance to decay by radioactive processes

What is irradiation

When an object is exposed to radiation / doesn't become radioactive

What is ionisation

Removing electrons from atoms to form ions / can mutate dna to cause cancer

Thomson's plum pudding model

Atom is a ball of positive charge with negative electrons / wrong

Nuclear Model (Rutherford)

Positive nucleus containing mass

Protons

Mass 1 / charge +1

Neutrons

Mass 1 / charge 0

Electrons

Mass small / charge -1

Alpha particles

5cm range in air / absorbed by paper and skin / high ionisation / 2 protons and 2 neutrons

Beta particles

1m range in air / absorb by 5mm aluminium / medium ionisation / high speed electron

Gamma particles

Unlimited range / absorbed by few cm of lead / low ionising / em wave

Energy levels

Absorbing radiation moves electrons away from the nucleus / emitting radiation brings electrons closer to the nucleus

Alpha decay

Mass number - 4 / atomic number - 2

beta decay

Atomic number increases by 1

Why is alpha radiation used in smoke detectors?

It ionises the air particles, causing a current to flow. If there is smoke in the air, it binds to the ions- meaning the current stops and the alarm sounds

Why are beta particles used to test metal sheets thickness

What is contamination

Radioactive particles getting onto objects

Radio isotopes

radioactive isotopes

What is emitted during radioactive decay

radiation

what was Rutherfords scattering experiment

small + particles fired at gold atoms / particles affected by gold foil atoms

If most of the particles went straight through the gold atoms in rutherfords experiment, what does that mean

Most of the atom is empty space

if some of the positive particles in Rutherfords scattering experiment were deflected, what does that mean

The nucleus is positive / deflects it

If a tiny number of particles rebounded backwards in Rutherfords scattering experiment, what does that mean

nucleus is small / holds mass

what is nuclear fission

The splitting of a nucleus to 2 smaller daughter nuclei and the release of 2/3 neutrons

How are control rods used in nuclear fission reactions

They absorb neutrons from each reaction to make sure only 1 goes on / fission neutrons collide with water molecules

How to calculate energy released in fission

mass lost during fission x speed of light (2)

How is energy made using nuclear reactors

nuclear fuel in a reactor creates steam / steam turns a turbine / turbine turns a large magnet in a coil of wire in a generator / passes electricity into a transformer to inc voltage

How does the sun produce energy

nuclear fusion of hydrogen nuclei to 1 helium atom / cause by high temp and pressure / emits a lot of energy

What is nuclear fusion?

two nuclei sticking together to form a new, heavier nucleus