Waves (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Flashcards

False.

The stopwatch starts when the second person sees the blocks being banged together, and stops when they hear the sound. This is because light travels much faster than sound.

In the echo method, a person stands about 50 m from a wall and claps blocks together in rhythm with the echoes. An average of 20 claps is taken to reduce timing errors.

The oscilloscope method is more accurate because the timing is done automatically by the oscilloscope, removing human reaction time errors.

In the stopwatch method, reaction time errors of up to 0.2 s are significant because the sound travel time may be as short as 0.3 s.

Amplitude is the distance from the undisturbed (rest) position to the peak or trough of a wave.

It is measured in metres (m).

To measure the speed of water ripples experimentally:

1. Two people stand a few metres apart; measure the distance between them with a tape measure

2. One person disturbs the water surface to create a ripple

3. The second person times how long the ripple takes to reach them using a stopwatch

4. Repeat 10 times and calculate an average

5. Calculate wave speed using speed = distance ÷ time

True.

A greater distance increases the time interval being measured, making the reaction time error (up to 0.2 s) a smaller proportion of the total time and improving accuracy.

On a wave diagram, the amplitude is measured from the undisturbed position to a peak or trough. The wavelength is measured from one peak to the next peak.

In the echo method, the total distance sound travelled is 20 × 2 × 50 = 2000 m.

Each clap-and-echo cycle covers 2 × 50 m (to the wall and back), and this is repeated for all 20 claps.

The purpose of the strobe light is to make the waves appear stationary by flashing at the same frequency as the waves.

This makes it much easier to measure the wavelength accurately using a ruler.

Complete the table for ripple tank equipment.

False.

The independent variable is frequency (set using the signal generator). The dependent variable is wavelength, which is measured as the frequency changes.

To measure wavelength in a ripple tank:

1. Use a ruler to measure the total length across several wavefronts on the screen

2. Divide this distance by the number of wavefronts

Measuring across multiple waves reduces the percentage uncertainty in the result.

True.

Recording with a video camera (with a ruler in frame) and pausing the footage allows wavefronts to be measured while stationary, removing the difficulty of measuring moving waves.

To measure frequency in the ripple tank experiment:

1. Count the number of wavefronts passing a fixed point over a measured time period

2. Divide the number of wavefronts by the time (in seconds)

Counting over a longer time period (e.g. 1 minute) reduces the effect of random errors.

In the ripple tank experiment, the control variables are the depth and temperature of the water.

One safety precaution:

Keep water and electrical equipment separated — working with water near electricity creates a risk of electric shock. Stand up throughout so you can react quickly to any spills, and do not consume food or drink near the equipment.

A stationary wave pattern (sometimes called a 'solid' wave) is when the wave appears not to be moving.

It forms when the frequency of the signal generator is set so that the string vibrates in a stable pattern of nodes and loops, making the wavelength easy to measure.

Amplitude is the distance from the undisturbed (rest) position to the peak or trough of a wave.

It is measured in metres (m).

To read amplitude from a displacement–distance graph, measure the distance from the centre line (undisturbed position) vertically up to the highest point (peak) or down to the lowest point (trough).

Wavelength is the distance from one point on a wave to the same point on the next wave.

For example, from one peak to the next peak. It is measured in metres (m) and given the symbol λ (lambda).

False.

Time period T = 1 / f = 1 / 4 = 0.25 s.

The period is the inverse of the frequency: a higher frequency means a shorter time period.

Frequency is the number of waves passing a point each second and is measured in hertz (Hz).

The time period (T) is the time taken for one complete wave to pass a fixed point.

It is measured in seconds (s) and is related to frequency by: T = 1 / f.

True.

Waves with a higher frequency have more oscillations per second, which means they transfer more energy per second.

The relationship between frequency and time period is:

T = 1 / f

where T is the time period in seconds (s) and f is the frequency in hertz (Hz). They are the inverse of each other — a higher frequency means a shorter time period.

A wave has a frequency of 50 Hz. Its time period is 0.02 s.

(T = 1 / 50 = 0.02 s)

The wave equation links wave speed, frequency, and wavelength:

v = f × λ

where v = wave speed (m/s), f = frequency (Hz), and λ = wavelength (m).

In the wave equation v = f × λ:

1. Wave speed (v) is measured in metres per second (m/s)

2. Frequency (f) is measured in hertz (Hz)

3. Wavelength (λ) is measured in metres (m)

Using v = fλ, frequency can be found by f = v ÷ λ and wavelength can be found by λ = v ÷ f.

False.

Using λ = v ÷ f: λ = 300 ÷ 100 = 3 m, not 30 m.

Always divide wave speed by frequency to find wavelength.

To calculate the wavelength:

Step 1: Find frequency: f = 1 / T = 1 / 2 = 0.5 Hz

Step 2: Use λ = v / f = 0.15 / 0.5 = 0.30 m

True.

Both transverse and longitudinal waves obey the wave equation v = fλ. It applies to all wave types, including sound, light, and water waves.

A frequency of 2 kHz is equal to 2000 Hz. A wavelength given in cm must be converted to metres before using v = fλ.

To calculate wave speed:

Step 1: Convert frequency: 0.5 kHz = 500 Hz

Step 2: Use v = f × λ = 500 × 0.6 = 300 m/s

Electromagnetic waves are transverse waves that transfer energy from a source to an absorber.

They can all travel through a vacuum and travel at the same speed (3 × 10^8 m/s) in a vacuum or air.

The order from longest to shortest wavelength (lowest to highest frequency) is:

1. Radio waves

2. Microwaves

3. Infrared

4. Visible light (red → violet)

5. Ultraviolet

6. X-rays

7. Gamma rays

False.

Radio waves have the longest wavelength (and lowest frequency). Gamma rays have the shortest wavelength and the highest frequency and energy.

Complete the table of electromagnetic wave uses.

Gamma rays, X-rays and ultraviolet radiation are considered harmful because they have high frequency and therefore high energy.

This makes them highly ionising — they can damage cells and tissues, increasing the risk of cancer.

True.

All electromagnetic waves travel at 3 × 10^8 m/s in a vacuum. This is a key shared property of the entire electromagnetic spectrum.

Visible light is the part of the electromagnetic spectrum that the human eye can detect.

It ranges from red (longest wavelength) to violet (shortest wavelength), and makes up only a tiny fraction of the full EM spectrum.

In visible light, red has the longest wavelength (and lowest frequency and energy), while violet has the shortest wavelength (and highest frequency and energy).

The colours in order are: red, orange, yellow, green, blue, indigo, violet.

Electromagnetic waves are transverse waves. They all travel at the same speed in a vacuum and form a continuous spectrum.

One use of microwaves: satellite communications (or cooking food).

One use of infrared: electrical heaters (or infrared cameras, or cooking food).

In both cases, the electromagnetic wave transfers energy from a source to an absorber.

The independent variable is the colour (and type) of surface on each flask. It is the factor deliberately changed to investigate its effect on infrared radiation emitted.

Filling the flasks with the same amount of water at the same starting temperature ensures these are control variables. This means any difference in cooling rate is due to the surface colour only, making the results valid.

In the infrared experiment, the black surface loses heat the fastest by radiation, while the silver surface loses heat the slowest.

True.

A black (or dull, dark) surface is a better emitter of infrared radiation than a silver (shiny) surface. This is why the black flask cools fastest in the experiment.

Plot temperature on the y-axis against time on the x-axis and draw curves of best fit for each flask. The flask with the steepest curve is losing heat the fastest by infrared radiation.

False.

Colour does not affect heat loss by conduction or convection. These are the same for every flask. Any difference in cooling between flasks is due to infrared radiation only.

A key systematic error is flasks starting at different temperatures. This can be reduced by coordinating in pairs to start all flasks simultaneously, and using a data logger with a digital thermometer for more accurate readings.

The resolution of the thermometer is 1°C. Resolution is the smallest change in a quantity that a measuring instrument can detect.

Radio waves are produced by oscillations in electrical circuits. An alternating current (a.c.) causes charges to oscillate, generating radio waves with the same frequency as the current.

True.

The frequency of the radio wave produced equals the frequency of the alternating current driving the transmitting antenna. This is the key relationship for radio wave production.

In a transmitting antenna, an alternating current causes charges to oscillate up and down. This produces radio waves with the same frequency as the oscillating current.

When radio waves are absorbed by a receiving aerial, they induce an alternating current with the same frequency as the incoming wave.

The absorbed radio wave oscillates back and forth, causing charges in the aerial to oscillate in the same way. This produces an alternating current with the same frequency as the received radio wave.

False.

A receiving aerial produces an alternating current, not a direct current. The oscillating radio wave causes charges in the aerial to oscillate, producing an a.c. with the same frequency as the wave.

Reflection occurs when a wave hits a boundary between two media and does not pass through. It stays in the original medium and bounces back. The wave changes direction but does not change speed or frequency.

False.

Electromagnetic waves can be reflected, refracted, transmitted, or absorbed at a boundary. What happens depends on the wavelength of the wave and the properties of the material.

How a substance interacts with an electromagnetic wave depends on the wavelength of the wave and the properties of the material.

The same material may absorb one wavelength, transmit another, and reflect a third. For example, glass transmits visible light but absorbs much of the infrared radiation that hits it.

Shiny (smooth) surfaces act as mirrors when they reflect waves, while rough surfaces scatter waves in all directions.

Glass transmits visible light but absorbs infrared radiation.

This is important in the greenhouse effect: short-wavelength radiation from the Sun passes through the atmosphere, but the longer-wavelength infrared re-emitted by the Earth's surface is absorbed by greenhouse gases.

False.

Rough surfaces are the least reflective. They scatter light in all directions rather than reflecting it in one direction. Shiny (smooth) surfaces are the most reflective because they act as mirrors.

When electromagnetic waves hit a boundary, the interaction depends on the wavelength of the wave and the properties of the substance.

Refraction is the change in direction of a wave when it passes from one medium to another. It occurs because the wave changes speed at the boundary between the two media.

Refraction is the change in direction of a wave caused by a change in the speed of the wave as it crosses a boundary between two different materials.

False.

During refraction, the frequency of the wave does not change. Only the speed and wavelength change. Since frequency stays the same, light does not change colour when it refracts.

During refraction, the speed and wavelength of the wave both change. The frequency stays the same. When a wave enters a denser medium, speed and wavelength both decrease.

When light travels from a more dense medium to a less dense medium, it bends away from the normal, and its speed increases.

One end of the wavefront enters the new medium and changes speed before the other end. This causes the wavefront to turn, changing the wave's direction. The greater the speed change, the greater the change in direction.

True.

When light moves from a less dense to a denser medium (e.g. air to glass), it slows down and bends towards the normal. The mnemonic is: Enters Towards.

As water waves move from deep to shallow water, the speed decreases and the wavelength decreases. The frequency remains the same. This is an example of refraction due to a change in depth.

The normal is a dashed line drawn perpendicular (at 90°) to the boundary at the point where the wave crosses. Angles of incidence and refraction are both measured from the normal.