Final Claude Year 10 Physics Exam Revision

What is the universe?

Definition: All of space, time, matter and energy that exists, including all galaxies

What is a star/sun?

Definition: A large luminous sphere of gas/plasma held together by gravity

What is a planet? What effect does it have on other objects?

• Definition: A large body of matter that orbits a sun

• Its gravity is large enough to clear the surrounding area of other objects

What is a galaxy? What are the types of galaxies?

Definition: A group of solar systems that are held together by a gravitational force

• Types: Spiral, elliptical, peculiar, irregular, barred spiral

• The Milky Way is a barred spiral

What is a solar system? What are the planets (in order) of our solar system?

• Definition: A series of planets and moons orbiting the same star/sun

• Memory cue: My Very Educated Mother Just Served Us Nachos

• Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

What is an Astronomical Unit?

• Definition: The distance from the Earth to the Sun (AU)

• Used to measure distances within our solar system

• EG Distance between planets, distance from the Sun to other planets

• 1 AU = 149,598,000 km

What is a light year?

• Definition: The distance light travels in one year (ly)

• 1 ly = 9.46 trillion km

• Used for distances to nearby stars

What is parallax? How is parallax used to measure the distance to stars?

• Definition: The apparent change in the position of an object when viewed by an observer from a different position

• Used to measure the distance to nearby stars

• Nearby stars show a larger apparent shift than distant stars

• The larger the parallax angle, the closer the star

How do you calculate distance using parallax?

• Distance (pc) = 1 ÷ parallax angle (arcseconds)

• e.g. parallax of 0.5 arcseconds: d = 1 ÷ 0.5 = 2.00 pc

What is a Parsec?

• Definition: The distance from an object whose parallax angle is 1 arcsecond (pc)

• 1 arcsecond = 1/3600th of a degree

• Generally measured from the sun to the object

• 1 pc = 3.26 light years (about 31 trillion km)

• Used for distances to stars and star clusters

What is a megaparsec?

• Definition: 1 million parsecs (Mpc)

• About 3.26 million light years

• Used for distances to galaxies and galaxy clusters

How do the AU, light year, parsec and megaparsec compare?

• Smallest to largest: AU → Light Year → Parsec → Megaparsec

• 1 ly ≈ 63,000 AU

• 1 pc = 3.26 ly

• 1 Mpc = 1,000,000 pc

How do you convert between astronomical units?

• To a bigger unit, divide, e.g. 6.52 ly ÷ 3.26 = 2.00 pc

• To a smaller unit, multiply, e.g. 2 pc × 3.26 = 6.52 ly

What does the colour of a star depend on? What can be determined from it?

• The colour of a star depends on its surface temperature

• From colour, its surface temperature can be found

• Hottest to coolest: blue → white → yellow → orange → red

• Most stars are either red or orange

What is the difference between luminosity and apparent brightness?

• Luminosity: a star's actual brightness (how much light it gives off)

• Apparent brightness: how bright the star looks from Earth

• Apparent brightness depends on the star's luminosity and its distance from Earth

What is the dispersion of white light?

• Definition: The process of white light dispersing into its different colours when it passes through a triangular glass prism

• White light contains all the colours of the visible spectrum

• Each colour is refracted (bent) by a different amount as it passes through the prism

• Causes the colours to spread out and form a spectrum

What colours does white light disperse into? How do their wavelength and frequency differ?

6 Colours: Red, Orange, Yellow, Green, Blue, Violet

Frequency increases and wavelength shortens moving from Red to Violet

What is an emission spectrum? How is it viewed and what can be determined from it?

• Definition: The unique pattern of narrow, discrete bands of coloured light produced when the light emitted by a heated element is separated

• When an element is heated, its atoms emit light which can be separated into narrow, discrete bands of colour

• The bands of colour are characteristic of that particular element

• An emission spectrum can be viewed using a spectroscope • Since every element has a unique emission spectrum, it can be used to identify the elements present

What is an absorption spectrum? What can be determined from it?

• Definition: The unique pattern of dark lines produced when white light passes through a cold gas element, and the gas absorbs specific wavelengths

• A cool element absorbs the same colours of light that it emits when heated

• Each element has a unique absorption spectrum

• An absorption spectrum can be used to identify the elements present in a gas or the outer atmosphere of a star

What do the dark bands of a star's absorption spectrum tell you compared to the emission spectrum of the same star?

• The dark bands occur at the same wavelengths as the bright lines in its emission spectrum

• This confirms the star's elemental composition, as each element has a unique pattern of spectral lines

What implication do red and blue shift have for the motion of stars relative to Earth?

• Red shift and blue shift show whether a star or galaxy is moving away from or towards Earth

• Red shift: Light is shifted towards the red end of the spectrum, indicating the star or galaxy is moving away from Earth

• Blue shift: Light is shifted towards the blue end of the spectrum, indicating the star or galaxy is moving towards Earth

• The greater the shift, the faster the object is moving

• Red and blue shift are caused by the Doppler effect

How do red and blue shift appear on a spectrum?

• The dark absorption lines move towards the red end (red shift) or blue end (blue shift)

• Compared to the lines for the same element measured on Earth

What is the Doppler effect? How does it explain the observations of red and blue shift?

• Definition: The apparent change in the wavelength and frequency of a wave caused by the relative motion between the source and the observer

• As a star or galaxy moves away from Earth its light waves are stretched, increasing their wavelength and causing a red shift

• As a star or galaxy moves towards Earth its light waves are compressed, decreasing their wavelength and causing a blue shift

• The greater the red or blue shift, the faster the object is moving relative to Earth

• Astronomers use the Doppler effect to determine the direction and speed of stars and galaxies

What key terms should you use when answering red and blue shift questions?

• Moving away from Earth → wavelength increases (stretched) → frequency decreases → red shift

• Moving towards Earth → wavelength decreases (compressed) → frequency increases → blue shift

• Always say the direction (moving away or towards) and what happens to BOTH wavelength and frequency

What does the Hertzsprung-Russell Diagram describe?

• Plots a star's absolute brightness (luminosity) against its surface temperature, which is determined from its colour

• Groups stars into: Main sequence, Giants, Supergiants, White dwarfs

How are the axes of the H-R diagram set out?

• Y-axis: luminosity, brightest at the top

• X-axis: surface temperature, decreasing from left (hot, blue) to right (cool, red)

What is the relationship between surface temperature and luminosity on the main sequence?

• The hotter the surface temperature, the greater the luminosity

• Main sequence runs from top left (hot, bright) to bottom right (cool, dim)

• Most stars are main sequence stars, where they spend most of their lives

Where are giants, supergiants and white dwarfs on the Hertzsprung-Russel diagram?

• Giants and supergiants: top right, cool but very bright because they are huge

• White dwarfs: bottom left, hot but dim because they are small

What colour and mass stars have hotter surface temperatures?

• Blue stars have hotter surface temperatures than red stars

• High-mass stars have stronger gravity, causing higher core temperatures

• This increases the rate of nuclear fusion, producing more energy

• Therefore, high-mass stars are hotter, brighter, and blue • Low-mass stars are cooler, dimmer, and red

What is the lifecycle of a star?

• All stars: Nebula → Protostar → Main Sequence

• Low-mass stars: Main Sequence → Red Giant → Planetary Nebula → White Dwarf

• High-mass stars: Main Sequence → Supergiant → Supernova → Neutron Star or Black Hole

• The mass of a star determines the path it follows after the main sequence stage

What is a nebula? How does it form a protostar?

• Definition: A giant cloud of gas (mostly hydrogen) and dust

• Gravity causes denser regions of the nebula to collapse and clump together

• Density and temperature increase as matter is pulled inward

• As the clump contracts further, it heats up and forms a protostar

What is a protostar? How does it form a main sequence star?

• Definition: The earliest stage star created from the collapse of gas and dust within a nebula

• Gravity continues pulling matter inward, causing the protostar to become more dense and hotter

• Pressure and temperature in the core continue to increase

• When the core becomes hot and dense enough, hydrogen nuclear fusion begins

• The protostar becomes a main sequence star

What stage do stars spend most of their lives in? What follows this stage?

• Definition: A stable star where hydrogen nuclei fuse into helium in the core, releasing energy

• Hydrogen fusion produces energy that creates outward pressure

• This balances the inward force of gravity, keeping the star stable

• The star remains in this stage for most of its lifetime

• When hydrogen in the core is depleted, the star evolves depending on its mass (low = red giant, high = supergiant)

What is a red giant? How do low mass stars become this?

• Definition: A low-mass star that expands after most hydrogen in its core has been used

• Hydrogen fusion in the core slows and eventually stops

• Gravity causes the core to contract, increasing its temperature

• The outer layers expand and cool, causing the star to become larger and redder

What is a planetary nebula? How does it form following red giants?

• Definition: A glowing cloud of gas released from a low to medium-mass star

• A red giant becomes unstable near the end of its life

• It ejects its outer layers of gas into space

• Radiation from the remaining hot core causes the gas to glow, forming a planetary nebula

What stage follows a star becoming a planetary nebula?

• A white dwarf follows the planetary nebula stage

• The remaining hot, dense core is left behind after the outer layers are expelled

• Nuclear fusion has stopped

• The white dwarf slowly cools over time

What are supergiants? How do high mass stars become this?

• Definition: Extremely large, luminous stars formed from high-mass main sequence stars

• High-mass stars use up their hydrogen fuel in the core

• The core contracts, causing temperature and pressure to increase

• The outer layers expand significantly, forming a supergiant

• The core begins fusing heavier elements

What is a supernova? How does it happen?

• Definition: A massive explosion of a supergiant star at the end of its life

• The core runs out of fuel and suddenly collapses

• The outer layers are blasted into space

• Releases huge amounts of energy and forms the heaviest elements

What are neutron stars? How do they form following supergiants?

Definition: An extremely dense star remnant made mostly of neutrons

• A high-mass star becomes a red supergiant and eventually undergoes a supernova

• The remaining core collapses under extreme gravity

• The pressure forces protons and electrons to combine, forming neutrons

• This creates a neutron star

What are black holes? How do they form following supergiants?

• Definition: An object with immense gravity where light can't escape

• A very high-mass star becomes a red supergiant

• The core runs out of fuel and can no longer support itself against gravity

• The core collapses, causing a supernova explosion

• If the remaining core is extremely massive, it collapses into a black hole

What decides if a star becomes a neutron star or a black hole?

• The mass of the core left after the supernova

• About 1.4 to 3 solar masses → neutron star

• More than about 3 solar masses → black hole

What is the largely discredited theory for the origin of the universe?

• The steady state theory

• States that the universe has no beginning and no end, where new matter is constantly created yet the universe's appearance remains the same

• Discredited as there was little evidence to support it

Why was the steady state theory discredited?

• Cosmic background radiation was discovered in 1965

• Steady state could not explain it, but the Big Bang predicted it

What is the widely accepted theory of the creation of the universe?

• The Big Bang Theory

• States that the universe began about 13.8 billion years ago from an extremely hot, dense state and has been expanding and cooling ever since

What is a singularity?

Definition: A point where all the matter and energy of the universe was condensed into an extremely small, hot and dense state

Describe how the Big Bang created the universe. How were the first stars formed?

• E = mc² shows that energy can be converted into matter (and matter into energy)

• In the early universe, energy formed matter and antimatter • Matter and antimatter annihilated, producing energy in the form of photons (energy particles)

• Slightly more matter than antimatter remained, which separated from the photons as it cooled and expanded

• This allowed protons and electrons to combine to form hydrogen atoms

• Gravity pulled hydrogen atoms together into clouds of hydrogen gas

• Increasing mass → gravity → pressure → temperature

• When the core became hot and dense enough, nuclear fusion began → the first stars formed

How does Einstein's famous equation help support the Big Bang Theory?

• E = mc² shows that energy can be converted into matter and matter can be converted into energy

• In the early universe, vast amounts of energy formed matter and antimatter

• Matter and antimatter annihilated, converting back into energy

• Slightly more matter than antimatter remained, allowing the universe to form

• Explains how matter could have formed after the Big Bang, supporting the Big Bang Theory

What are the 4 pieces of evidence that support the Big Bang Theory?

• Cosmic background radiation

• Red-shifted light from galaxies

• Presence of primordial elements

• The formation of galaxies over time

How does cosmic background radiation provide evidence to support the Big Bang theory? (1 of 4)

• The energy from the initial expansion of the universe still exists

• It has cooled and now exists as electromagnetic microwaves throughout the universe

• How it supports: It is evidence of leftover energy from the universe's beginning

How does red-shifted light from galaxies provide evidence to support the Big Bang theory? (2 of 4)

• Light from other galaxies is red shifted, showing that galaxies are moving away from us

• The further away a galaxy is, the faster it is moving away

• How it supports: Shows the universe is expanding

How does evidence of primordial elements provide evidence to support the Big Bang theory? (3 of 4)

• The first atoms to form were the simplest elements (hydrogen)

• Heavier elements formed when stars collapsed

• The current ratio of light to heavy elements supports the universe being about 13.7 billion years old

• How it supports: The observed element ratios match its predictions

How does the process of galaxy formation provide evidence to support the Big Bang theory? (4 of 4)

• Galaxies formed and evolved over time as the universe expanded

• The formation of heavier elements in stars is similar to the formation of the first elements during the Big Bang

• This shows that galaxies continued to evolve over time, as predicted by the Big Bang Theory

What 3 conclusions did Edwin Hubble make about the movement of galaxies?

• Distant galaxies are receding (moving away) from Earth

• The further away a galaxy is, the faster it is moving away

• The universe is expanding

How do you answer calculation questions?

• Write the formula first

• Substitute the values you are given, with units

• Then rearrange (if that is the easiest way)

• Give all working and answers to 2 decimal places, with units

• Green CAS: press the two arrows going away from each other (<>) to expand the decimal

What are the formulas for speed and velocity?

• Speed = distance ÷ time • Distance = speed × time

• Time = distance ÷ speed

• Velocity: v = s ÷ t (s = displacement)

What are the formulas for stopping distance?

• Stopping distance = reaction distance + braking distance

• Reaction distance = speed × reaction time

What is the formula for acceleration?

• a = (v − u) ÷ t

• v = final velocity, u = initial velocity, t = time

What are the formulas for force and weight?

• Net force: Fnet = ma

• Rearranged: a = F ÷ m, m = F ÷ a

• Weight: W = mg (g = 9.81 m/s²)

What are the formulas for work and energy?

• Work: W = F × d

• GPE: Eg = mgΔh (mass in kg x acceleration due to gravity (9.8 m/s²) x vertical displacemnent in m)

• Kinetic energy: Ek = ½mv²

• Velocity from kinetic energy: v = √(2Ek ÷ m)

How do you calculate speed?

Definition: A measure of the distance travelled per unit of time

Measured in km/h or m/s

Speed = distance ÷ time • e.g. 100 m in 20 s: speed = 100 ÷ 20 = 5.00 m/s

How is average speed different to instantaneous speed?

• Average speed: A measure of how fast an object moves overall whilst ignoring all stops and changes in speed during the journey

• Average speed = total distance ÷ total time

• Instantaneous Speed: A measure of how fast an object moves at a particular moment during travel

• Can be seen in a speedometer

How do you convert between km/h and m/s?

• km/h → m/s: divide by 3.6 (larger to smaller unit = divide)

• m/s → km/h: multiply by 3.6

• e.g. 72 km/h ÷ 3.6 = 20.00 m/s

• e.g. 20 m/s × 3.6 = 72.00 km/h

What is a vector vs scalar quantity?

• Vector quantities: Have magnitude and direction

• Represented by arrows that can be added or subtracted

• Scalar quantities: Have only magnitude (size)

What are examples of vector and scalar quantities?

• Vector: Displacement, velocity, acceleration, force, momentum, weight

• Scalar: Time, distance, speed, mass, temperature, density

How is distance different to displacement?

• Distance: The actual length of path covered EG 300 m

• Displacement: The change in position and direction of an object EG 300 m North/from home to school

• Include the direction of displacement using true bearings EG 067°T

How do you show direction with positive and negative signs?

• Pick one direction as positive, e.g. North = +

• The opposite direction is negative, e.g. South = −

• So 4 m N is the same as −4 m S

How do you write displacement using bearings?

• Give the size and the direction, e.g. 300 m on a bearing of 067°T

• True bearings: measured clockwise from North, always 3 digits, written with °T

• Compass bearings: start from N or S and turn towards E or W, e.g. N67°E is the same as 067°T

• Draw a North arrow at the start point, then measure the angle clockwise to the line joining start and finish

How do you calculate displacement with bearings?

• e.g. walk 3 km North, then 4 km East

• Size: Pythagoras, √(3² + 4²) = 5.00 km

• Angle from North: tan⁻¹(4 ÷ 3) = 53.13°

• Displacement = 5.00 km on a bearing of 053.13°T

How do you calculate distance and time from speed?

• Distance = speed × time, e.g. 15 m/s for 4 s = 15 × 4 = 60.00 m

• Time = distance ÷ speed, e.g. 200 m at 8 m/s: t = 200 ÷ 8 = 25.00 s

Why is reaction distance different to braking distance? What is stopping distance?

• Reaction distance: The distance the car travels from the point at which a hazard is detected until it begins braking or swerving

• Braking distance: The distance the car travels from the point at which it begins braking until it comes to a stop

• Stopping distance = Reaction distance + braking distance

How do you calculate reaction distance?

• Reaction distance = speed (m/s) × reaction time (s)

• e.g. 20 m/s × 1.5 s = 30.00 m

• Doubling the speed doubles the reaction distance

What are the factors that affect stopping distance in terms of reaction distance?

• Level of tiredness

• Whether driver is under the influence of alcohol

• The drivers' awareness/hazard detection

• The effect of medication

• Psychological reaction time

• The vehicle's speed

What are the factors that affect stopping distance in terms of braking distance?

• The vehicle's speed (quadratically increases each time by a power of 2)

• EG 2 x higher speed = 2², 4x longer braking distance, 3x higher speed = 3², 9x longer braking distance

• The road's gradient and conditions

• The vehicle load EG Trucks have long braking distances

• The brakes (condition, braking technique and number of wheels braking)

How is velocity different to speed?

• Speed: The distance travelled per unit time (in km/h or m/s) EG 5 m/s

• Velocity: The rate of change of displacement over time EG 5 m/s East

• The direction of an object's velocity is the same as its displacement

How do you calculate velocity?

• Velocity = displacement (s) ÷ time (t)

• e.g. 150 m North in 30 s: v = 150 ÷ 30 = 5.00 m/s North

What are the units for motion quantities?

• Distance/displacement: m or km

• Time: s or h

• Speed/velocity: m/s or km/h

• Acceleration: m/s²

What does the gradient of a displacement/position-time graph give you?

• Displacement/position-time graph: Gives you velocity EG m/s North

• Velocity = displacement ÷ time

• A negative gradient gives you movement in the opposite direction

• Distance-time graph: gradient = speed

What do the shapes on a distance/position-time graph mean?

• Straight sloped line = constant speed

• Steeper line = faster

• Flat (horizontal) line = stationary (no movement)

• Curved line = speeding up or slowing down

What does the gradient of a velocity-time graph give you?

• Velocity-time graph: Gives you acceleration EG m/s² North

• Upward slope = accelerating

• Downward slope = decelerating

How is a flat line on a velocity-time graph different to a flat line on a position-time graph?

• Velocity-time graph: flat line is not no movement, it is constant velocity

• Position-time graph: flat line means the position is not changing, so the object is stationary

How do you tell from a velocity-time graph if an object is speeding up or slowing down?

• Velocity and acceleration in the same direction (same sign) = speeding up

• Velocity and acceleration in opposite directions (opposite signs) = slowing down

• e.g. v = +10 m/s, a = −2 m/s² → slowing down

• e.g. v = −10 m/s, a = −2 m/s² → speeding up (in the negative direction)

How do you calculate displacement using a velocity-time graph?

• Area under a velocity-time graph = displacement

• Calculate the total area between the plotted line (velocity) and x-axis (time) • Rectangle sections: time × velocity

• Sloped sections: area of a triangle = ½ × base × height

• Areas above the axis are positive (forward displacement) and areas below are negative (displacement in the opposite direction)

• Area under a speed-time graph = distance travelled

How is acceleration different to velocity?

Velocity: The rate of change of displacement over time

Acceleration: The rate at which velocity changes over time

How do you calculate acceleration?

• Acceleration = change in velocity ÷ change in time

• a = (v − u) ÷ t

• v = final velocity, u = initial velocity, t = time

• Measured in m/s²

• e.g. 5 m/s to 25 m/s in 4 s: a = (25 − 5) ÷ 4 = 5.00 m/s²

How is positive acceleration different to negative acceleration?

• Positive acceleration: acceleration in the positive direction

• Negative acceleration: acceleration in the negative direction

• Negative acceleration only means slowing down if the object is moving in the positive direction

• e.g. 10 m/s to 0 m/s in 5 s: a = (0 − 10) ÷ 5 = −2.00 m/s² (slowing down)

What is the acceleration of gravity?

• The acceleration of gravity (g) is 9.81 m/s² (when the effects of friction are not considered)

• All objects experience the same acceleration

• g can vary slightly on different points on the Earth's surface EG Decrease in high altitudes

What is a force?

Definition: A push or a pull that acts upon an object as a result of its interaction with another object

• Vector quantity, can cause an object to accelerate, change velocity, or change shape

• Unit for force is newtons (N)

What is 1 newton?

Definition: The force needed to accelerate a 1 kg mass at 1 m/s²

What are some of the types of forces classified as contact and non-contact?

Contact: Driving force, frictional force, drag/air resistance force, normal force, compression force, tension force

Non-contact: Magnetic force, gravitational force, electrostatic force

What is normal force?

Definition: The force applied by a surface at right angles to the surface in response to a push on it by an object

What are resistance forces?

Definition: Forces that oppose motion, including drag and frictional forces such as air resistance

• Drag is the force that opposes an object moving through a fluid (a liquid or a gas)

• EG Force of water against you as you swim

What are thrust or driving forces?

Definition: Forces that cause an object to move or accelerate forward

• EG Force of cars/planes engines or the force of a person pushing on the pedals of a bike

How are resistive forces different to thrust/driving forces?

• Resistive forces oppose the motion of an object

• Thrust/driving forces promote motion and move the object forward

What are tension and compression forces?

Definition: The forces caused by pulling on an object to stretch it or pushing on an object to compress it

• Tension force commonly exists in ropes and wires used to move objects or hold them stationary

What is the force of friction?

Definition: A resistance force created whenever two surfaces move or try to move across each other

• Friction always opposes the motion of one surface across another surface

• Friction is dependent on the texture of the two surfaces

What is the force of air resistance?

Definition: The force of air particles that oppose the motion of an object through the air

• It acts in the opposite direction to the object's velocity

• Air resistance increases with the speed of the object and its surface area

• A type of drag force (since air acts as a fluid (a gas))

What is mass?

Definition: A measure of the amount of matter in an object (kg)

• Mass is constant regardless of location

What is weight?

Definition: A measure of the force exerted on an object due to gravity (the force with which the Earth attracts you to its centre)

• Weight is a force (measured in newtons)

How is weight different to gravitational force?

• Weight is the gravitational force acting on an object

• Gravitational force refers to the attractive force between two masses, not just the force acting on an object near a planet

• Weight is dependent on the object's mass and the acceleration due to gravity (therefore Fnet = ma, W = mg)

How do you calculate the force of gravity (weight) at the Earth's surface?

• W = F = mg

• m = mass (kg), g = 9.81 m/s²

• e.g. a 60 kg person: W = 60 × 9.81 = 588.60 N