Fiches Physique GCSE : 53 termes clés, pour Brainlag Flashcards et Anki

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Isotopes

Have the same number of protons but different numbers of neutrons

Radioactive decay

Some nuclei are unstable. To become more stable they give out radiation

Activity

The rate at which nuclei in a source decay, measured in becquerels: 1 Bq is one decay per second.

Count rate

The number of decays it detects each second or minute.

Background radiation

Radiation is always around us from rocks, the air and space

Ionising

Knocking electrons off atoms.

Battery

Two or more cells joined together.

Ammeter

Measures current. It goes in series, in the same loop as the component.

Voltmeter

Measures potential difference. It goes in parallel, across the component's two ends.

Current

The rate of flow of charge: how many coulombs pass a point each second.

Potential difference

The push that drives charge through it. It tells you how much energy each coulomb of charge transfers: 1 volt is 1 joule per coulomb.

Resistance

How much a component opposes the current.

Ohmic conductor

For a fixed resistor at constant temperature the current is directly proportional to the p.d.

Kinetic energy store

Anything moving

Gravitational potential energy store

Anything raised up

Elastic potential energy store

Anything stretched or squashed

System

Just the object or group of objects you choose to look at.

Specific heat capacity

The energy needed to raise the temperature of 1 kg of a substance by 1 °C.

Work done

Energy transferred by a force.

Dissipated

Usually into the thermal store of the surroundings, where it spreads out and is no longer useful.

Non-renewable

Coal, oil, natural gas (the fossil fuels) and nuclear fuel. They are being used up faster than they can be replaced, and will run out.

Renewable

Wind, solar, hydroelectricity, tides, waves, geothermal and bio-fuel. Nature replaces them as fast as we use them.

Reliable (energy resource)

It can produce electricity whenever it is needed.

Scalar

A quantity with a size only

Vector

It has a size and a direction

Displacement

How far you end up from the start, in a straight line, and in which direction.

Contact forces

Need the objects to touch: friction, air resistance (drag), tension, the normal contact force from a surface, and upthrust in a fluid.

Non-contact forces

Act across a gap: gravitational force (weight), magnetic force and electrostatic force.

Centre of mass

The weight of an object acts as if it all pulls at one point

Resultant force

The single force that would have the same effect.

Resolving

Splitting one force into two parts at right angles.

Normal

An imaginary line at 90° to a surface, drawn where the ray hits it.

Specular reflection

A smooth surface (a mirror, still water) reflects parallel rays in a single direction, so you see a clear image.

Diffuse reflection

A rough surface (paper, a matt wall) scatters parallel rays in many directions.

Filter

Transmits its own colour and absorbs the rest.

Permanent magnet

Makes its own magnetic field all the time.

Induced magnet

A piece of magnetic material that becomes a magnet only while it sits in a field.

Magnetic field

The region round a magnet where a magnetic material or another magnet feels a force.

Alternating current (a.c.)

Its potential difference keeps swapping direction, so the current flows one way, then the other, many times a second.

Earth wire

A safety wire joined to any metal case. It is at 0 V and only carries a current if something goes wrong.

Transverse wave

The vibrations are at right angles to the direction the energy travels.

Longitudinal wave

The vibrations are along the same direction the energy travels.

Amplitude

The biggest displacement from the rest position, measured from the middle line to a crest.

Wavelength

The distance from a point on one wave to the same point on the next, such as crest to crest.

Frequency

How many waves pass a point each second, in hertz (Hz).

Period

The time for one complete wave to pass, in seconds.

Random error

Scatters readings both ways by different amounts (reaction time, a flickering display).

Systematic error

Shifts every reading the same way by the same amount.

Zero error

A systematic error: the instrument reads something when it should read zero.

Satellite

Anything that orbits a larger body.

Nebula

A cloud of dust and gas pulled together by gravity.

Galaxy

A huge group of billions of stars held together by gravity.

Light-year

The distance light travels in one year.