Physics (paper 1) Flashcards
What are the function of waves?
They transfer energy and information without transferring matter
Wavelength (λ)
Minimum distance in which a wave repeats itself
What is a wavelength measured in?
Metres
Amplitude (A)
Distance between the origin and the crest/trough
Frequency (f)
Number of waves that pass a point in a second
Frequency and wavelength are
inversely proportional
• High frequency = short wavelengths
• Low frequency = long wavelengths
How is the wavelength measured in transverse and longitudinal waves?
Transverse waves:
From one peak/crest to the next
Longitudinal waves:
From the centre of one compression to the next centre of compression
Time period (T)
The time taken for a single wave to pass a point
Wave velocity (speed)
The distance travelled by a wave each second
Transverse wave
Waves where the particles move perpendicular to the direction of energy transfer (oscillating motion)
Examples of transverse waves
• Ripples on the surface of water
• S - waves
• Electromagnetic waves (eg radio, light, x rays)
Longitudinal wave
Wave where the particles vibrate parallel to the direction of energy transfer (side to side motion)
What type of wave can travel through a vacuum?
Electromagnetic waves
When the points are close together in a longitudinal wave
Compression
When the points are spaced apart in a longitudinal wave
Rarefaction
Examples of longitudinal waves
• Sound waves
• P - waves
• Ultrasound
• Infrasound
Equations for wave speed (m/s)
• v = x/t
(Wave speed = distance/time)
• v = f x λ
(Wave speed = frequency x wavelength)
How do you work out wavelength? (λ)
Length x 2
Seismic wave
Wave produced by earthquakes
Types of wave interactions through an interface
• Reflection
• Refraction
• Transmission
• Absorption
Materials interact differently with waves depending on the wave’s ______
wavelength
Reflection definition
The bouncing back of a wave at a boundary
Refraction definition
When a wave changes speed at the boundary between materials of different densities
Transmission definition
When a wave passes through a substance
Absorption definition
When energy is transferred from the wave to the particles of a substance
What’s an echo?
Sound waves being reflected off a surface
How do waves get reflected?
(effect)
• Flat surfaces are the most reflective
(The smoother the surface, the stronger the reflected wave)
• Light will reflect if the object is opaque
• Electrons absorb the light energy and re emit it as a reflected wave
What does it mean if an object appears yellow?
• Only yellow light has been reflected
• All other wavelengths of visible light have been absorbed
What happens when waves speed up?
• The frequency stays the same
• The wavelength increases (gets longer)
• The waves travel away from the normal
What happens when waves slow down?
• The frequency stays the same
• The wavelength decreases
• The waves travel toward the normal
What is a normal
A line drawn perpendicular to an interface
Sound waves definition
The vibrations of molecules
Regions of higher and lower density in a longitudinal wave
Higher density: Compression
Lower density: Rarefaction
Range of frequencies humans can hear
20 Hz to 20,000 Hz
Ultrasound
Sound waves with a frequency above the human hearing range of 20000 Hz
Infrasound
Sound waves with a frequency below the human hearing range of 20 Hz
Explain the way the human ear works
• Vibrations in the air travels down the auditory canal causing the eardrum to vibrate
• Vibrations are passed onto the three small bones
• These bones amplify vibrations and transmit them to the liquid in the cochlea
• Tiny hairs in the cochlea detect vibrations and create electrical impulses
• They travel along neurones in the auditory nerve to the brain
Incident angle
Angle of the entering ray
What is the angle of reflection?
The angle of the exiting ray
Can sound waves travel through a vacuum? Explain.
• No. Longitudinal waves rely on vibrating particles to travel
• In a vacuum there are no particles to vibrate, and so sound waves can’t be transmitted.
How is ultrasound used in sonar?
• Ultrasound is emitted from a boat and travels towards the sea bed
• Ultrasound reflects off the sea bed and is detected by the boat
• The time between emission and detection is recorded
• This can be used to find out the depth of seabed
Ultrasound uses
• Foetal scanning
• Sonar
• echo location
Infrasound uses
• Exploration of the Earth’s core
• Detecting seismic activity
How is ultrasound used for foetal scanning?
• A transducer produces and detects a beam of ultrasound waves in body
• Ultrasound waves are bounced back to the transducer by different boundaries
• The echo reaches the transducer causing it to generate electrical signals to send to the scanner
• The detector calculates the tissue’s distance from transducer using speed and time
• Time measurements are used to build up an image
Why is ultrasound a safe method for foetal scanning compared to eg X rays?
• x rays are ionising whereas ultrasound isn’t
• Therefore x rays could damage tissue and mutate cells
What is applied during foetal scanning and why?
Gel is applied to ensure ultrasound is absorbed not reflected off your body
How is infrasound used in the exploration of the earths core?
• Earthquakes produce P-waves and S-waves
• These pass through the Earth’s centre and can be detected using seismometers
• The location and magnitude can be identified after carefully timing the arrival of its waves
Characteristics of P-waves
Primary waves
• Longitudinal waves
• Faster than S-waves so are felt first during an earthquake
• Produce a forward and back motion
• Can pass through solids and liquids
• Are very low frequency sound waves (infrasound)
Characteristics of S-waves
Secondary waves
• Transverse waves
• Slower than P-waves so are felt after them during an earthquake
• Produces a side to side motion
• Can only travel through solids
• Unable to travel through the Earth’s molten outer core
Method to calculate wave speed by measuring the frequency
• Measure the frequency by counting the number of waves that pass a ping on the harbour each second
• Measure the wavelength by counting the number of waves between two point on the harbour and dividing the distance by the number of waves
[][Topic5][]
Concave meaning
Curving inwards
Convex meaning
Curving outwards
Focal length
The distance between the centre of the lens and the focal point
Real image
An image that is formed where the rays of light are focused and come together
Virtual image
An image where rays of light appear to come but don’t in reality
Incident ray
Light ray moving towards a boundary
Law of reflection
Angle of incidence is equal to the angle of reflection
Why might the angle of reflection have a range of values when being measured in a practical?
The light beam may have been wide
Properties of red light in terms of waves
• Has the longest wavelength
• Has the lowest frequency
Properties of violet light in terms of waves
• Has the shortest wavelength
• Has the highest frequency
White light is
a combination of all the wavelengths of light
Black is
the absence/ absorption of light
What colour would a blue object appear through a green filter and why?
• Black
• Blue light is being absorbed so no light is being transmitted making it appear black
What is the critical angle?
The angle of incidence that gives an angle of refraction of 90°
What is Total Internal Reflection?
• When all the light is reflected back into the denser medium
• No refraction occurs
Criteria for Total Internal Reflection to occur
• The rays of light must travel from a more dense to less dense medium
• The angle of incidence must be greater than the critical angle
If the angle of incidence is less than the critical angle…
The light ray is refracted (away from the normal)
If the angle of incidence is equal to the critical angle…
• The light ray is refracted at 90° to the normal
• Therefore it’ll travel along the surface of the denser medium
Converging lens is another name for
Convex lens
What do convex lens do to light?
They refract parallel rays of light inwards into a single point (aka focal point)
What do concave lens do to light?
They refract parallel rays outwards
The shorter the focal length…
The more powerful the lens are
How do you make a lens more powerful without changing the focal length?
Make the lens more curved
How is an image formed?
When all the light rays from a point on an object come together
Inverted images are always
Real
Virtual images are always
Upright
Convex lens can produce
Real or virtual images
Concave lens always produce
Virtual images
Magnification equation
Image height / Object height
What happens when a ray of light travels perpendicular to a boundary?
The direction doesn’t change since it’s travelling along the normal
What is the critical angle of glass?
42°
What do all electromagnetic (EM) waves have in common?
• They are transverse waves
• They travel at the speed of light
What are the 7 waves on the EM spectrum?
• Radiowaves
• Microwaves
• Infra red rays
• Visible light waves
• Ultraviolet rays
• X-rays
• Gamma rays
What EM wave has the longest wavelength?
Radiowaves
What EM wave has the highest frequency and energy?
Gamma rays
How are gamma rays produced?
By changes in the nucleus of an atom
What are the 3 ionising EM waves?
• UV rays
• X-rays
• Gamma rays
What is the impact of ionising waves?
They can damage/mutate cells and therefore cause cancer
Uses of radiowaves
• Communications
• Satellite transmissions
• TV broadcasting
Uses of microwaves
• Heating food
• Mobile phone and satellite communication
Uses of infrared
• Remote control
• Night vision
• Electrical heaters
• Cooking
Uses of visible light waves
• Helps us see
• Photography
Uses of ultraviolet
• Fluorescent bulbs
• Getting a suntan
Uses of x-rays
• Used to image luggage and broken bones
Uses of gamma rays
• Sterilising medical equipment
• Treating cancer
Danger of microwaves
They heat up cells
Danger of infrared
It can cause skin burns
Dangers of ultraviolet
• Causes damage to skin cells (leading to cancer like X-rays and gamma rays)
• Can cause blindness
What is diffuse reflection?
• When light is reflected off a surface and is scattered in different directions
• Common in rough surfaces
What is specular reflection?
• When light rays reflect at the same angle they hit the surface
• Common in smooth surfaces like mirrors
Radiowaves can be created using what type of current?
Alternating current
What is an oscilloscope?
• A device that allows us to see the frequency of the alternating current
• This helps us determine the frequency of the radio wave
What would happen to an object if it emits more energy than it absorbs?
It would lose energy and cool down
What would happen if an object emits and absorbs the same amount of energy?
It would stay the same temperature
Intensity meaning
The power of radiation per unit area
What type of EM waves are included in a diagram of emitted radiation?
• UV radiation
• Visible light
• Infrared radiation
(in order of increasing wavelength)
What effect does the temperature of an object have on intensity?
• As the temperature increases, the intensity of every emitted wavelength increases
• With the shorter wavelengths increasing at a higher rate
Why does the colour of a Bunsen burner flame change as it gets hotter?
• The hotter the flame, the shorter the wavelength of light emitted
• Colour changes from orange to blue
What is the emitted radiation for an object at room temperature?
• Infra red radiation
• Not also visible light because we can’t see the emitted radiation
First atom model
• Dalton’s billiard ball model
• Tiny sphere that couldn’t be broken up
What atom model did JJ Thompson propose?
• The plum pudding model
• A dough of positive charge with negative electrons in it
What atom model did Rutherford propose?
• Nuclear model
• Positively charged nucleus surrounded by a cloud of negative electrons
What atom model did Bohr propose?
• The Bohr model
• Electrons orbit the nucleus at fixed distances called energy levels or shells
[] What is the equation for calculating speed?
• v (m/s) = x (m) / t (s)
• Average speed = total distance / time taken
Equation for calculating acceleration
• a (m/s²) = /\ v (m/s) / t (s)
• a = v - u
———
t
• change in velocity / time taken
• final velocity - initial / time
Equation for calculating uniform (constant) acceleration
• a = v² - u² / 2x
• (final speed)² - (initial speed)² / 2 x distance travelled
When the resultant force is 0N, what does it indicate about an object?
The object is either moving at constant speed or is stationary
Newton’s first law for a stationary object
If the resultant force on a stationary object is zero, the object will remain at rest
Newton’s first law for a moving object
If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction)
What is the equation for force?
Mass x Acceleration
Newton’s second law of motion
The acceleration of an object is directly proportional to the net force and inversely proportional to its mass (f= ma)
Weight meaning
Force acting on an object due to gravitational attraction
Newton’s third law
Whenever two bodies interact, the force they exert on each other are equal and opposite
How do you calculate momentum?
Mass x Velocity
p (kg m/s) = m (kg) v (m/s)
(p = mv)
Conservation of momentum
Total momentum before a collision = total momentum after a collision
Other ways of calculating force
(mv - mu) / t
=
(m △v) / t
=
△p /t
Is momentum a scalar or vector quantity?
Vector
How is momentum conserved in a collision?
• P = mv
• The forces exerted by both objects are equal and opposite (3rd law)
• Force of X on Y = -force of Y on X
• So change in momentum of X = -change in momentum of Y
• Y accelerates because of force from X
• So total momentum before collision = total momentum after collision
When does the momentum of an object change?
• If an object accelerates / decelerates
• If it changes direction
• If its mass changes
Equation for weight
W = mg
(mass x gravitational field strength)
Closed system meaning
When the energy within an object/ objects is constant and there is absence of external forces (eg friction)
Force definition
Rate of the change in momentum
• /\ p / /\ t
• (change in momentum / change in time)
Stopping distance meaning
The total distance travelled during the time it takes for a car to stop in response to emergency
Equation for stopping distance
SD = Thinking distance + Braking distance
Thinking distance meaning
The distance travelled during the driver’s reaction time
(in metres)
Braking distance meaning
The distance travelled under the braking force
(metres)
Factors that affect thinking distance
• Tiredness
• Excessive drug/ alcohol intake
• Poor visibility
• Speed
Factors that affect braking distance
• Icy/wet roads
• Speed
• Mass of car
• Condition of tyres/brakes
Equations for braking distance
• Ek / f
• = 1/2mv² /ma
How is energy transferred as a car brakes?
Energy is transferred from kinetic energy to sound and thermal energy
Work done by brakes is equal to
The kinetic energy of the car
Equation that shows that the work done is the transfer of kinetic energy
Braking force x Braking distance = 1/2 x mass x velocity² (kinetic force)
In elastic collisions, what happens to kinetic energy?
Kinetic energy is conserved
In inelastic collisions, what happens to kinetic energy?
Kinetic energy changes (usually decreases)
Why does an object accelerate during circular motion?
• The direction of the object is constantly changing
• Therefore the velocity is changing as it’s a vector
• Because acceleration is the rate of change of velocity it would also change
What does M mean eg in or MHz or MW?
• Mega
• 10^6
What does G mean eg in GHz or GW?
• Giga
• 10^9
Centripetal force meaning
The perpendicular force acting towards the circle’s centre that keeps an object in uniform circular motion
What factors affect the size of a centripetal force?
• Mass
• Acceleration
Typical walking speed
1.5 m/s
Typical running speed
3 m/s
Typical cycling speed
6 m/s
Speed of sound
330 m/s
Typical person’s reaction time
0.2s - 0.9s
Describe Rutherford’s Alpha Particle Experiment
• A beam of alpha particles (He 2+ ions) was directed at a thin gold foil
• He discovered that:
• Most of the particles passed straight through the metal (showing atoms are mostly empty space)
• Some alpha particles were deflected as they repelled (showing how the nucleus of atoms have strong positive charge)
• Very few of the particles bounced back (showing that atoms contain a small, heavy nucleus)
What conditions were required for Rutherford’s experiment?
• Thin gold foil was used rather than thick
• So particles were able to pass through it
• The chamber was evacuated
• The air was removed so none of the alpha particles would collide with anything before reaching the foil
What is radioactivity?
When an unstable nucleus loses energy as it emits radiation
What are the 3 types of radiation?
• Alpha particles
• Beta particles
• Gamma radiation
Ionising radiation meaning
• When radiation has enough energy to remove an electron from the shell of an atom
• Dangerous as it causes DNA damage and cancer
How do we measure/detect radiation?
• We use a GM tube (Geiger Muller) and counter
• We place the source in front of the GM tube and every time it clicks it measures the number of radiations per second
Radiation meaning
The giving off of excess energy
Unit for radiation
Becquerel (Bq)
Alpha particles characteristics
• 2+ charge (Helium nucleus)
• Mass of 4 (2 protons and neutrons)
• Stopped by skin or a sheet of paper
• Most ionising power
• Only travels a few cm
Beta particle characteristics
• Charge of -1
• (fast moving electron)
• Mass of 0
• Stopped by a sheet of aluminium
• Moderate ionising power
• Can travel up to a metre
Gamma radiation characteristics
• Type of wave
• Charge and mass of 0
• Stopped by thick sheets of lead/concrete
• Weak ionising power
• Most penetrating
• Can travel long distances
• Travels at speed of light
Irradiation meaning
When someone is exposed to ionising radiation but doesn’t come into contact with it
Contamination meaning
When someone comes into contact with radioactive isotopes
Protective measures to reduce exposure to sources
• Long tongs to handle source
• Lead aprons/ protective masks
• Stand behind barriers
• Personal radiation monitor
Background radiation
Exposure to ionising radiation at low levels form naturally radioactive substances
Sources of background radiation
• Radon gas from rocks (50%) (trapped in earth)
• Cosmic rays
• Gamma rays from ground and buildings
Approximate size of an atom
1 x 10^-10 m
What is alpha radiation used for?
• Fire alarms
• Alpha source in fire alarm causes ionisation and current
• Smoke particles stop the current causing the alarm to sound
What is beta radiation used for?
• Thickness control for paper/aluminium as they partially absorb it
• If the amount of detected radiation changes, thickness has changed so rollers are adjusted
What is gamma radiation used for?
• Detecting leaks in underground pipes
• Sterilise medical equipment as it kills microbes
• Detecting cancer
Radioactive decay is…
random
Equation linking acceleration, distance and velocity
v² - u² = 2ax
Nanometres to metres
1 x 10 ^ -9
Possible reasons to why there are limits to the frequencies the human ear can detect
• Eardrum not sensitive enough to detect low/high frequencies
• Brain cannot interpret low/high frequencies
What happens in a nuclear decay?
The mass (nucleon) number, atomic number and charge is conserved
What happens in an alpha/beta decay?
The nucleus transmutes into another element and both the atomic & mass number changes
What takes place during beta - decay?
• A neutron in the nucleus of an atom turns into a proton and electron
• The electron leaves the nucleus
• The atomic number increases by 1 as there’s one more proton
What takes place during beta + decay?
• A proton in the nucleus turns into a neutron and positron
• The positron leaves the nucleus
• The atomic number decreases by 1 as there’s one less proton than before
Equation for beta - decay
1 1 0
n —-> p + β
0 1 -1
Equation for beta + decay
1 1 0
p —-> n + β
1 0 +1
Half-life definition
Time it takes for activity rate to half
(The time it takes for half of the radioactive nuclei in a source to decay)
Formula for activity rate
A = Ao (original activity)
——-
2^n (number of half lives)
What happens during gamma radiation?
• Gamma is a wave that carries energy away from the nucleus
• Therefore proton and mass number stay the same
Medical tracer meaning
A radioactive isotope that can be used to track the movement of substances in the body eg blood
Why are gamma emitters used as a tracer?
• They’re highly penetrating and are able to pass through body whilst still being detected outside body
• They have low ionising levels so any harm to the patient is minimal
Why is it beneficial for isotopes to have short half lives when being used as a tracer?
• So its unlikely to cause long term damage to the patient
• Whilst still being able to take an image before radioactivity decreases
What is PET (Positron Emission Tomography)?
• Positrons are emitted as the tracer decays
• They travel a small distance and annihilate (get converted) when they interact with electrons in the tissue
• A pair of gamma rays are produced and can be detected outside the body
Nuclear fission meaning
The splitting of a large, unstable nucleus into 2 smaller nuclei (usually uranium-235)
What happens during nuclear fission?
• A slow moving neutron is fired at a nucleus
• The nucleus absorbs the neutron and becomes unstable
• The nucleus splits into 2 smaller (daughter) nuclei
• 2/3 rapid neutrons and a lot of energy are released
Purpose of nuclear reactor
• Converts energy from nuclear fission into electricity
• They produce energy at the correct rate if the number of neutrons in the reactor is constant
How does chain reactions occur?
• The new neutrons from previous fission can be absorbed by another nucleus and start another fission reaction which creates excess neutrons
Purpose of chain reactions
They keep nuclear reactors running
Purpose of control rods in nuclear reactor
• Control chain reactions
• They absorb neutrons without becoming unstable themselves
• Made of boron material
Purpose of moderator in nuclear reactors
• Slow neutrons produced by fission down to maintain chain reaction
• Made of water/graphite
Nuclear fusion meaning
When 2 light nuclei join to form a heavier nuclei
Nuclear fusion characteristics
• Light nuclei are both positively charged so they repel
• Requires extremely high temperatures to overcome repulsion
• Stars use nuclear fusion to produce energy
Comparing nuclear fusion and nuclear fission
• Both produce large amounts of energy
• Nuclear fission requires a neutron
Why does light intensity decrease as it travels between different boundaries?
Light is always reflected when it passes through a boundary so some energy gets lost
Practical for measuring the critical angle using a semi circular glass
• Shine a ray of light into the block through curved face
• Change angle until angle of refraction = 90°
• Measure angle of incidence when refracted angle is 90° using a protractor
• Repeat measurement of critical angle
Comparing radiowaves and gamma rays
• Radiowaves are created by oscillations of moving electrons
• Are produced by humans
• Are produced in electrical currents
• Gamma rays may result from radioactive decay
• Gamma rays are produced to stabilise nucleus
• Produced by annihilation in PET
