0625 Physics Lecture Notes

These flashcards cover key concepts, definitions, and principles from the 0625 physics syllabus, including topics in motion, forces, energy, thermal physics, waves, electricity, magnetism, nuclear physics, and space physics.

Scalar Quantity

A quantity that has magnitude only.

Vector Quantity

A quantity that has both magnitude and direction.

Speed

Distance travelled per unit time.

Velocity

Speed in a given direction.

Acceleration

Change in velocity per unit time or rate of change in velocity.

Deceleration

Decrease in velocity per unit time or rate of decrease in velocity.

Mass

Measure of the quantity of matter in an object at rest relative to the observer.

Weight

Gravitational force on a mass or effect of a gravitational field on a mass.

Gravitational field strength

Force per unit mass, equivalent to the acceleration of free fall.

Density

Mass per unit volume.

Spring constant

Force per unit extension.

Limit of proportionality

Point up to which extension is directly proportional to the load.

Hooke’s law

Extension is proportional to the load applied, up to the limit of proportionality.

Centre of gravity

Point where all the weight of an object seems to act.

Moment of a force

The turning effect of a force, product of force and perpendicular distance from the pivot.

Principle of moments

Sum of clockwise moments about a point is equal to the sum of anticlockwise moments about the same point.

Momentum

Product of mass and velocity.

Principle of conservation of momentum

If objects collide, the total momentum before the collision is the same as the total momentum after, provided no external forces act.

Impulse

Product of force and time for which force acts.

Resultant force

Change in momentum per unit time.

Principle of conservation of energy

Energy cannot be created or destroyed; it can only be transformed between energy stores.

Work done

Product of the force and displacement moved in the direction of the force.

Power

Work done per unit time or energy transferred per unit time.

Efficiency

Ratio of the useful power output to the total power input.

Pressure

Normal force acting per unit area.

Absolute zero

Lowest possible temperature (−273°C) where particles have least kinetic energy.

Boyle’s law

For a fixed mass of gas at constant temperature, the product of pressure and volume is constant.

Specific heat capacity

Energy transferred per unit mass per unit temperature change.

Boiling point

Temperature at which liquid becomes a gas.

Evaporation

Process where water molecules with more energy escape from the surface.

Wavefront

Imaginary surface that connects crests or troughs in a wave.

Wavelength

Distance between two adjacent crests or troughs.

Frequency

Number of complete oscillations per unit time.

Amplitude

Maximum displacement of a point of the wave from the equilibrium position.

Wave speed

Distance travelled by the wave per unit time.

Transverse wave

A wave where the direction of vibration is at right angles to the direction of propagation.

Longitudinal wave

A wave where the direction of vibration is parallel to the direction of propagation.

Normal

A line drawn perpendicular to the surface.

Angle of incidence

Angle formed between incident ray and normal.

Angle of reflection

Angle formed between reflected ray and normal.

Law of reflection

Angle of incidence is equal to the angle of reflection.

Refractive index

The ratio of speed of light in vacuum to its speed in a specific medium.

Critical angle

Angle of incidence at which the angle of refraction is exactly 90°.

Total internal reflection

All light is reflected when angle of incidence is greater than critical angle.

Focal length

Distance between centre of the lens and principal focus.

Principal axis

Line passing symmetrically through the optical centre of the lens.

Principal focus (focal point)

The point at which rays of light parallel to the axis converge after passing through a lens.

Virtual image

An image that cannot be projected onto a screen and light only seems to come from it.

Monochromatic light

Light of a single frequency.

Long sightedness

Condition where image focuses behind retina, corrected by converging lens.

Short sightedness

Condition where image focuses in front of retina, corrected by diverging lens.

Digital signal

A signal that consists of two values.

Analogue signal

A signal that varies over a range of values.

Compression

Region where particles are close together or region of higher than normal pressure.

Rarefaction

Region where particles are further apart or region of lower than normal pressure.

Echo

Reflection of sound waves.

Ultrasound

Sound with a frequency higher than 20 kHz.

Magnetic field

Region in which a magnetic pole experiences a force.

Electric field

Region in which an electric charge experiences a force.

Electric current

Charge passing a point per unit time.

Direct current

Flow of electric charge in only one direction.

Alternating current

Direction of the current constantly reverses.

Emf (electromotive force)

Electrical work done by a source in moving a unit charge around a complete circuit.

Potential difference

Work done per unit charge in passing through a component.

Kilowatt-hour

Amount of electrical energy transferred by a 1 kW appliance in one hour.

Potential divider

Circuit arrangement that splits e.m.f. between resistors in series.

Resistance

Ratio of voltage across a component to the current flowing through it.

Ohm’s law

Current through a conductor is proportional to potential difference when at constant temperature.

Nucleon number

Total number of protons and neutrons in a nucleus.

Proton number

Total number of protons in a nucleus.

Nuclear fusion

Process where two small nuclei join to form a bigger nucleus, releasing energy.

Nuclear fission

Process where a large unstable nucleus splits into smaller nuclei, releasing energy.

Isotopes

Same element with different number of neutrons and the same number of protons.

Background radiation

Radiation from natural sources, always present in the environment.

Half-life

Time taken for half the nuclei of a sample to decay.

How a protostar is formed (a-b)

A protostar is an interstellar cloud (of gas and dust that contain hydrogen) collapsing and increasing in temperature as a result of its internal gravitational attraction

How a protostar becomes a stable star (c)

When the inward force of gravitation attraction is balanced by an outward force due to the high temperature in the centre of the star.

How red giants / supergiants are formed (d-e)

Once stars eventually run out of hydrogen as fuel for the nuclear reaction in the centre of the star, and most has been converted into helium, they expand to form red giants/supergiants(massive stars).

Red giant path → ? (f)

Red supergiant path → ? (g-h)

Red giant forms a planetary nebula with a white dwarf star at its centre.

Red supergiant explodes as a supernova, forming a nebula containing hydrogen and new heavier elements, leaving behind a neutron star or a black hole at its centre. This nebula may form new stars with orbiting planets.

Milky Way

One of the many billions of galaxies making up the Universe, and it’s diameter is approximately 100 000 light-years

Feature of the Sun

A star of medium size, consisting mostly of hydrogen and helium, that radiates most of its energy in the infrared, visible light, and ultraviolet regions of the electromagnetic spectrum.

Galaxy

Collection of billions of stars.

Light-year

Distance travelled in the vacuum of space by light in one year, used to measure astronomical distances. (9.5×10^15 m)

Redshift

Increase in observed wavelength of electromagnetic radiation from receding stars and galaxys. Is evidence that the universe is still expanding, and supports the Big Bang Theory.

CMBR

Cosmic Microwave Background Radiation: Microwave radiation of a specific frequency is observed at all points in space around us, and was produced shortly after the Universe was formed.

How to determine the:

1) Speed at which a galaxy is moving away from the earth

2) Distance of a far galaxy from earth

1) Change in wavelength of the galaxy’s starlight due to redshift

2) Brightness of a supernova in that galaxy

Hubble constant, H0

Ratio of the speed at which a galaxy is moving away from Earth to its distance from Earth.

What does formula 2 represent + what is H0

Hubble’s constant = 2.2 × 10^-18

1/H Represents an estimate for the age of the universe and is evidence for the idea that all the matter in the universe was present at a single point