3.1 Waves & The Electromagnetic Spectrum

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.

Different types of waves are used in hospitals.

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. 

Explain why the technician uses the value in the equation.

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.

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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.

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. 

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. 

A sound wave and a radio wave have the same wavelength.
    
State why they have different frequencies. 

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.

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The table shows the main sections of the electromagnetic spectrum.

 

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

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. 

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

 

A teacher demonstrates different types of wave.  

She uses a spring to demonstrate longitudinal waves.

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.

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. 

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.

(1)

(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

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.

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.