Waves and the Electromagnetic Spectrum

Question 1

How do waves begin?

Answer 1

Waves begin with some kind of oscillation or vibration

Question 2

What do waves transfer?

Answer 2

Energy from place to place, not matter

Question 3

What are waves?

Answer 3

A wave is a vibration that transfers energy from place to place without matter being transferred

Question 4

What are the two types of wave?

Answer 4

Transverse waves: the energy is being transferred from left to right, while the particles are going up and down. Oscillations are perpendicular to energy.
Longitudinal waves: the energy is being transferred from left to right, and the particles are moving back and forth in the direction of the wave. Oscillations are parallel to energy.

Question 5

What is a time period?

Answer 5

Time period: time taken for a wave to move one whole wavelength past a certain point, or the time taken for one complete oscillation.
Frequency: the number of wavelengths that go past a certain point every second.

Question 6

What is the wave equation?

Answer 6

Frequency = 1 / Time period
F = 1/T

Question 7

What are wavelengths, frequencies and velocities?

Answer 7

Wavelengths: the distance between two peaks/ troughs on a wave
Frequency: the number of wavelengths that go past a certain point every second
Velocity: the speed of a wave

Question 8

What is the equation linking velocity, frequency and wavelength?

Answer 8

Velocity (m/s) = frequency (Hz) x wavelength (m)
Frequency = velocity / wavelength
Wavelength = velocity / frequency

Question 9

What is the electromagnetic spectrum?

Answer 9

Transverse waves that all travel at the speed of light. There are seven types of radiation: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. They are the only types of wave that can travel through a vacuum.

Question 10

What are radio waves? How do they affect the body? How are they used?

Answer 10

Electromagnetic waves with the lowest wavelength and energy. They are transmitted through the body without being absorbed. They can be produced in an electrical circuit with an alternating current. These are transmitted to a receiver, where they are absorbed, forming an alternating current in that circuit. This has the sane frequency. Long wave radio waves can bend around the surface of the Earth. Short range radio waves can also be received at long distances as they are reflected by the atmosphere. They are sometimes used by satellites.

Question 11

What are microwaves? How do they affect the body? How are they used?

Answer 11

Waves with longer wavelengths than radio waves but shorter than X-rays. Some wavelengths can be absorbed by the body, heating cells, which can be dangerous. They are used in microwave ovens as they can penetrate somewhat into food before being absorbed and transferring their energy into water molecules in food. Other wavelengths can pass through the Earth’s watery atmosphere so can be picked up by satellites, which transmit the signal back in a different direction.

Question 12

What are X-rays? How do they affect the body? How are they used?

Answer 12

They are high frequency EM waves. They are ionising, so can mutate and damage the body. They have lots of energy and can pass through the skin. They are transmitted by soft tissue and are absorbed by denser tissue like bones, so are used in X-rays. It is directed through the body or object onto a detector plate. Brighter parts are where fewer X-rays get through, producing a negative image on photographic paper. They are used in airport security scanners.

Question 13

What is infrared radiation? How do they affect the body? How are they used?

Answer 13

A type of thermal EM radiation emitted by all objects. It is mostly reflected or absorbed by skin, heating cells, so can cause burns. It is given out more by hotter objects, so infrared cameras can monitor temperature (thermal imaging). This is used by police and security systems. It causes objects to get hotter, so is used by electric heaters. It is used to transfer information over short distances e.g. TV remotes. Optical fibres carry info over long distances using infrared radiation using total internal reflection.

Question 14

What are ultraviolet waves? How do they affect the body? How are they used?

Answer 14

EM waves after visible light. They are absorbed by the skin and are ionising, so can cause damage to skin cells (potentially skin cancer) and eye cells. They are used in fluorescent lamps, where UV is used to emit visible light. They are energy efficient. They are also used for security pens (secret ink) and detecting forgeries on bank notes and passports. They can sterilise water.

Question 15

What is visible light?

Answer 15

EM waves detected by the eye. The colours go: red, orange, yellow, green, blue, indigo, violet, with red with the longest wavelength and violet with the shortest. It is used to illuminate things and photography.

Question 16

What are gamma rays? How do they affect the body? How are they used?

Answer 16

They have the smallest wavelengths and highest frequencies in the electromagnetic spectrum. They are ionising and transfer the most energy of all EM waves, so they can pass through skin to deeper tissue, causing mutations and cancers. They kill microbes, so are used to sterilise food and medical equipment. They are used in cancer treatments and tracers.

Question 17

What are sound waves?

Answer 17

Longitudinal waves carried by compressions and rarefactions of the air (or other medium). The speed of sound depends upon the type, pressure and temperature of the medium it is travelling through. In dry air at 20 degrees the speed of sound is 343m/s.

Question 18

How our sounds produced? What do their amplitudes and frequencies mean?

Answer 18

They are produced when objects vibrate.

The bigger the vibration (amplitude), the louder the sound. The higher the frequency, the higher the pitch of the sound.

Question 19

What is a sonic boom?

Answer 19

A loud noise produced by an object travelling faster than the speed of sound, created because of the shock waves being compressed together by the speed of the object.

Question 20

What is ultrasound and how is it used?

Answer 20

A high frequency sound wave that is inaudible to humans, and is quite safe. It has a frequency of 20,000 Hz and above. We cannot feel its vibrations. As it can pass through the body and is reflected by an unborn baby at boundaries it can create an image based on speed and time. It is also used in industry to find flaws in materials, as cracks reflect waves sooner.

Question 21

What is SONAR?

Answer 21

It stands for sound navigation and ranging. A sound wave is released and is reflected by whatever it hits. Detecting it when it comes back (time) will tell you how far away something is (distance = time x speed). If molecules are close together in a substance then it will travel fast.

Question 22

What is infrasound and how is it used?

Answer 22

If sound is lower than 20 Hz it is infrasound. We cannot hear this, but sometimes we can feel it. Some animals communicate with it e.g. elephants and whales, so we can track them for conservation reasons. It is produced before volcanoes erupt, earthquakes, hurricanes, meteors, and tsunamis, so we can use them to predict disasters.

Question 23

What is foetal scanning?

Answer 23

Ultrasound waves are produced by a transducer probe, which also receives the sound waves. Some ultrasound waves are reflected at each boundary between different tissues or organs, which allows the image to be created. As we know the speed of sound in human tissue and the time it takes, we can see how far apart different tissues are. Gel is used between the ultrasound probe and the skin to get the gel to pass through.

Question 24

What is a reverberation?

Answer 24

A phenomenon that can happen when sound waves reflect off surfaces in a small room. It creates the sense of a prolonged sound, as the brain keeps sound in memory for a short period of sound. If the sound reflects and reaches the brain before it is out of memory it creates the illusion of sound lasting longer. If the sound reaches the brain after this time it is heard as an echo.

Question 25

What waves are released by earthquakes?

Answer 25

P-waves: primary waves. They are longitudinal and can travel through solids and liquids. They are faster than S-waves (5-8km/s)
S-waves: secondary waves. They are transverse and can only travel through solids. They are slower than P-waves (2.5-4km/s)
L-waves: love waves. They are neither transverse nor longitudinal but 3D waves, difficult to predict and cause earthquakes. They are the fastest surface waves.

Question 26

How did we determine the structure of the Earth’s core?

Answer 26

The speed of seismic waves varies in different densities, so we can use this to determine the boundaries between different layers. Both P- and S-waves travel through the mantle, which tells us that it is solid (mostly), but S-waves do not travel through the outer core, so it must be liquid.

Question 27

How can we measure the speed of sound?

Answer 27

Attach a signal generator to a speaker to generate sounds with a specific frequency. Use two microphones and an oscilloscope, attaching them so the detected waves are shown separately. Put one next to the speaker and move the others so they are aligned and have moved one wavelength apart. Measure the distance between the microphones to find one wavelength. Use this and the frequency to find the speed of sound.

Question 28

How can we measure the speed of water ripples?

Answer 28

Use a signal generator attached to the dipper of a ripple tank to create water waves at a set frequency. Dim the lights and turn on a strobe light so you can see a wave pattern on the screen below. Adjust the frequency of the strobe light until the wave pattern on the screen appears to stop moving - this is when the frequency matches that of the waves. Measure the distance between lines 10 wavelengths apart, then find the average. Use the formula to calculate wave speed.

Question 29

How can we find the speed of waves in solids?

Answer 29

Measure and record the length of a metal rod. Attach it to a clamp with elastic bands next to a microphone. Tap the rod with a hammer and write down the peak frequency on the computer. Repeat this to get an average. Calculate the wave speed using the equation, where the wavelength equals twice the length of the rod.

Question 30

What can happen to waves at boundaries?

Answer 30

Absorbed - the wave transfers energy to the material, often by heat e.g. in microwaves
Transmitted - the wave carries on travelling through, often leading to refraction
Reflected - the wave is sent back away from the material e.g. echoes

Question 30

What is refraction?

Answer 30

When a wave enters a new material it changes speed depending on the new density. If it hits the boundary at an angle this change of speed causes a change in direction. If it slows down (enters a denser material) it bends towards the normal

Question 31

How do we hear?

Answer 31

Sound waves reach the eardrum and cause it to vibrate. The vibrations are sent to tiny bones called ossicles, through the semicircular canal and to the cochlea. The cochlea turns these vibrations into electrical signals which are sent to the brain. The brain interprets the sound. Hearing is limited by the size and shape of the eardrum and structure of the ear.

Question 32

How does radiation affect the Earth’s temperature?

Answer 32

The Sun transfers energy to the Earth in the day. This is reflected and absorbed by the Earth’s atmosphere, clouds and surface. Most is absorbed, increasing local temperature. At night radiation is emitted by the atmosphere, clouds and surface, decreasing local temperature. The overall temperature stays fairly constant.

Question 33

How can you test how well different surfaces emit radiation?

Answer 33

Wrap four identical test tubes with the same material e.g. paper. They should have different surfaces or colours e.g. black, white, glossy, and matte. Fill them with the same amount of hot water and measure the temperature decrease over time. The better the emitter, the quicker the temperature decrease. Matte and black surfaces are better emitters.

Question 34

How does EM radiation emitted change with temperature?

Answer 34

As the temperature of an object increases, the intensity of radiation emitted increases. The peak wavelength (wavelength with the highest intensity) decreases. This means objects appear brighter and less red.