# AQA Core Physics 1b - Radiation and the Universe.

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AQA Core Physics 1b - Radiation and the Universe.

Electromagnetic Waves.

Electromagnetic waves are things like radio waves, microwaves and x-rays.

Electromagnetic Waves Carry Energy but Not Matter.

1) Electromagnetic radiation travels as electromagnetic waves (EM waves).

2) Like other waves, they transfer energy from one place to another without moving any matter.

All Waves Have Wavelength, Frequency, Amplitude and Speed.

If you look at the waves on a beach, they vary in height and in how far apart they are. Some travel faster than others, and some slow down as they get nearer the beach.

1) WAVELENGTH is the distance from one peak to the next.

2) FREQUENCY is how many complete waves there are per second (passing a certain point). It's measured in hertz (Hz). 1 Hz is 1 wave per second.

3) AMPLITUDE is just the height of the waves from the mid line to the peak.

4) The SPEED is just how fast it goes.

There's a Continuous Spectrum of EM Waves.

EM waves with different wavelengths (or frequencies) have different properties. We group them into seven basic types, but the different regions actually merge to form a continuous spectrum.

They are group together below, with the increasing frequency (decreasing wavelength) starting from bottom to top:

frequencytype of electromagnetic radiationtypical usewavelength highest gamma radiation killing cancer cells shortest X-rays medical images of bones ultraviolet detecting forged bank notes by fluorescence visible light seeing infrared optical fibre communication microwaves cooking lowest radio waves television signals longest

1) All the different types of electromagnetic waves travel at the same speed in a vacuum (e.g. space).

2) EM waves with higher frequencies have lower wavelengths.

Wave Speed = Frequency x Wavelength.

Speed = Frequency x Wavelength.

(m/s) = (Hz) x (m) OR

V = Velocity.

Example: A radio wave has a frequency of 92.2 x 10 to the power of 6 Hz. Find it's wavelength. (The speed of all EM waves is 3 x 10 to the power of 8 m/s)

USE THE TRIANGLE!

Answer: Your trying to find the wavelength using f and v, so rearrange the equation.

So wavelength = v / f = 3 x 10/ 9.22 x 10= 3.25m.

Different types of Em radiation have very different properties. E.g. Radio waves pass through bones by X - rays don't.

EM Radiation can be Absorbed, Reflected or Transmitted.

1) The different wavelengths of EM radiation interact different with matter. When a wave meets some matter, like air or glass, three things can happen:

• The radiation might be transmitted and just pass through the substance, as light passes through glass.
• It could be reflected, bounce back, like light reflected from a mirror.
• Or the radiation could be absorbed, the energy of the wave is transferred to the matter.

2) Two or three of these things can happen at the same time. E.g. when sunlight shines on glass a lot of light passes through, but some of it is reflected. Which is why you can see your reflection in the glass.

3) What happens to the radiation depends on…