Waves & The Electromagnetic Spectrum (Edexcel IGCSE Physics (Modular): Unit 2)

Microwaves are part of the electromagnetic spectrum.

Which part of the electromagnetic spectrum has longer wavelengths than microwaves? 

The diagram shows part of a water wave.  

Which letter represents the wavelength? 

The diagram shows a water wave.

What is the wavelength of the wave?

The table shows the main sections of the electromagnetic spectrum.

The arrow below the table shows the direction of

Which of these electromagnetic radiations has a frequency greater than ultraviolet?

The diagram shows a wave on the sea.

Which letter shows the wavelength of the wave?

Water waves are transverse waves. Other waves can be longitudinal.

State a similarity and a difference between a transverse wave and a longitudinal wave. 

A student writes some sentences about electromagnetic waves. Their teacher underlines a mistake in each sentence.

In the table, write a suitable correction for each mistake.

The first one has been done for you. 

Gamma radiation is used in hospitals even though it can be dangerous. 

Describe one use of gamma radiation in hospitals.

(i) Explain the risks to patients and doctors of using gamma radiation.

(2)

(ii) State one way of reducing the risks to a doctor who uses gamma radiation.

(1)

The table shows the main sections of the electromagnetic spectrum.

(i) State two sections of the spectrum that are used for communications.

(2)

(ii) State two sections of the spectrum that are used for cooking.

(2)

A radio station broadcasts at a frequency of 200 kHz.      The wavelength of the radio waves is 1500 m.

 (i) State the equation linking wave speed, frequency and wavelength. 

(1)

(ii) Calculate the speed of these radio waves and give the unit.

(3)

 speed = ...................... unit ........

The chart lists some electromagnetic radiations.

Complete the table by giving one radiation from the chart from each use.

You may give each radiation once, more than once, or not at all.

William Herschel was a scientist who investigated infrared radiation. He passed electromagnetic radiation from the Sun through a triangular glass prism. The prism refracted different radiations by different amounts.

The paths of yellow and blue visible light rays are shown in the diagram.

Add to the diagram to show how the prism refracts an infrared ray.

A pulsar is a type of star.

    We receive radiation from a pulsar in regular short bursts called pulses.

Some pulsars emit radio waves. Other pulsars emit x-rays. 

 (i) State a property of waves that is the same for radio waves and x-rays.

(1)

(ii) State two properties of waves that are different for radio waves and x-rays.

(2)

The graph shows five pulses of the signal from a pulsar. 

(i) Use the graph to estimate the average time between each pulse. 

(2)

(ii) Calculate the frequency of the pulses in the signal.

    Give the unit.

(2)

 frequency = .......................... units ...........

A teacher demonstrates different types of wave.  

She uses a spring to demonstrate longitudinal waves.

 (i) Draw arrows on the diagram to show the directions in which the teacher moves her hand.

(1)

(ii) Give an example of a longitudinal wave.

(1)

The teacher then demonstrates transverse waves.

   She fixes a vertical rod in a pond. She places a small wooden ring on the rod.

  The ring floats on the water and moves up and down the rod as waves go past.

 (i) On the diagram, draw a line to show one wavelength.

   Label your line with the letter W.

(1)

(ii) The distance from P to Q is 5.0 cm.

   Determine the amplitude of the wave.

(1)

(iii) The wooden ring reaches point P every 15 s.

Calculate the frequency of the wave.

Give the unit. 

(3)

 frequency = ....................... unit ...........

(iv) Explain how the movement of the wooden ring demonstrates that this wave is transverse.

(2)

(v) The wave shown is a water wave.

Give a different example of a transverse wave.     

(1)

Some waves travel across the sea.

They all have the same wavelength.

What is meant by the term wavelength?

The waves travel across the sea at 3.0 m/s and have a frequency of 1.5 Hz. 

(i) State the equation linking wave speed, frequency and wavelength.

(1)

(ii) Calculate the wavelength of the waves

(2)

  wavelength = ........................... m

The diagram represents a microwave travelling in free space from point A to point B.

The distance from A to B is 0.60 m.

Calculate the wavelength of this microwave.

wavelength = ................................ 

(i) State the equation linking wave speed, frequency and wavelength.

(1)

(ii) Calculate the frequency of this microwave.

[speed of microwave in free space = 3.0 × 10⁸ m/s]

(3)

A microphone is connected to an oscilloscope to display a sound wave.

The diagram shows the trace on the oscilloscope screen.

The oscilloscope settings are:

Y direction: 1 square = 1 V

X direction: 1 square = 0.001 s

(i) How many time periods are shown on the trace?

(1)

(ii) What is the frequency of the sound wave?

(2)

On the grid below, sketch the trace of a sound wave with a smaller amplitude and a higher frequency than the wave shown by the dotted line.

In 1901, Marconi received the first radio signal across the Atlantic Ocean.

The frequency of Marconi’s radio wave was 820 kHz and the wavelength was 366 m.

(i) State the equation linking wave speed, frequency and wavelength for radio waves.

(1)

(ii) Calculate the speed of the radio waves Marconi received.

(2)

speed of radio waves = .................................. m/s

Some people do not believe that Marconi received 820 kHz radio waves.

They think that the frequency was really twice as much: 1640 kHz.

If these people are correct, what wavelength radio waves did Marconi receive?

wavelength = .......................... m

Other people do not think Marconi received a radio signal across the Atlantic Ocean at all.

They think the radio waves he received were really caused by electrostatic discharges from storm clouds.

Explain what happens when a storm cloud discharges.

A scanner uses one type of wave to check for broken bones.

An image of the bone is seen because the waves from the scanner are  

Ultrasound waves are also used to produce images.

This is an ultrasound image of a fetus surrounded by fluid. 

The ultrasound image is caused by waves which bounce off the fetus.

This is an example of waves that are 

A student has some LEDs connected in a circuit. They emit light of different colours.

The different colours of light are waves which must have:

A remote control emits infrared waves to operate a television.

The television receives infrared waves and radio waves.

It emits light waves and sound waves.

Which type of wave has the highest frequency?

A student is listening to a radio. 

The radio is powered by batteries that provide a direct current (d.c.).

What is direct current? 

Radio waves are part of the electromagnetic spectrum.

(i) Suggest a property of radio waves that makes them suitable for use in communication.

(1)

(ii) Complete the table to show uses and possible harmful effects of some other parts of the electromagnetic spectrum. 

(4)  

Different types of waves are used in hospitals.

(i) Draw a line linking each type of electromagnetic wave with its use.

(2)

(ii) Electromagnetic waves are transverse.

Describe how the vibrations of a transverse wave relate to the direction in which the wave travels.

(1)

Another type of wave used in hospitals is ultrasound. Ultrasound waves are used to make images of internal organs.

    A scanner emits an ultrasound wave into the patient and records any reflections. 

 (i) The scanner records the time from when a wave is emitted to when its reflection is received.                 

A technician calculates the depth of the reflection using the equation

  Explain why the technician uses the value in the equation.

(2)

(ii) An ultrasound wave travels faster in the patient than it does in air.

Explain how a change in speed affects the wavelength of the ultrasound wave.

(2)

Name one type of wave that is used in cancer treatment and explain what it does during the treatment.

Ultrasound waves are sound waves with a very high frequency. They are often used for medical purposes.

Dentists use ultrasound waves to clean patients’ teeth.

The diagram shows an ultrasound cleaner removing plaque from teeth.

The tip of the ultrasound cleaner vibrates 96 million times per second and is sprayed with water.

(i) State the frequency of the ultrasound emitted by the cleaner and give the unit.

 (2)

 frequency = ....................... unit .....

(ii) Suggest how the cleaner removes plaque.

(1)

(iii) Suggest why water is sprayed on the tip of the cleaner. 

(1)

(i) State the equation linking wave speed, frequency and wavelength.

(1)

(ii) The ultrasound waves have a wavelength of 0.00044 m and travel at a speed of 1540 m/s in the fluid.

Calculate the frequency, in MHz, of the ultrasound waves.

(3)

Other waves also have medical uses.

Ultraviolet waves are used by doctors to cure some skin conditions.

Suggest two differences between ultrasound waves and ultraviolet waves.

An LED needs a minimum voltage to make it emit light.

The student investigates this minimum voltage using the circuit shown.

The student uses a voltmeter to measure the voltage across the LED.

Add this voltmeter to the circuit diagram.

The student gradually increases the voltage across the LED and records the minimum voltage at which the LED emits light. 

The results for some different LEDs are shown in the table.

Display the results of the student's investigation on the grid.

The student concludes:

Evaluate the student's conclusion.

Waves can travel on water, through air or in a vacuum.

The diagram shows the side-view of a wave on the surface of water.

Each square on the grid represents 1 cm x 1 cm. 

 (i) State the wavelength of the wave shown. 

(1)

(ii) On the grid sketch the trace of a wave travelling at the same speed, but with a larger amplitude and a lower frequency.  

(2)

Two students investigate the speed of sound waves in air.

They use a stopwatch that shows times to the nearest 0.1 s.

They use an outdoor running track as their measure of distance.

The track is straight and 100 m long.

Describe what else they must do to obtain a value for the speed of sound. 

(i) State the equation linking wave speed, frequency and wavelength. 

 (1)

(ii) The speed of radio waves is 300 000 000 m/s.

A radio wave has a frequency of 31 MHz. Calculate the wavelength of this radio wave.  

(3)

 wavelength = .......................... 

A sound wave and a radio wave have the same wavelength.     

State why they have different frequencies.