# Physics Unit 3, Revision Notes

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X-rays 4

Ultrasound 4

Lenses 5

Ray diagrams 5

The eye 6

Total internal reflection 7

Moments 7

Hydraulics 8

Pendulums and circular motion 8

Magnetic fields 9

Electric motors 9

Transformers and Power 10

# X-rays

• The electromagnetic spectrum consists of visible light, radio waves, microwaves, infrared and x-rays. All these waves are transverse waves travelling at the same speed in a vacuum.
• We see how the shorter the wavelength the higher amount of energy transferred. Gamma rays, X-rays and ultraviolet rays have enough energy to remove electrons from atoms/molecules and form ions. This is known as ionisation. Ionising radiation can harm the body by killing cells leading to cancer.
• Properties of X-rays include:
• They affect a photographic film in the same way as light (turn black)
• They are absorbed by metal and bone and are transmitted through some materials that are opaque to visible light.
• they are transmitted by soft tissue
• their wavelength is of the same order of magnitude as the diameter of an atom
• Newer X-ray machines use charge-coupled devices (CCDs) instead of photographic film, CCD converts light to electrical signals which can be recorded in a computer’s memory.
• Computerized tomography (CT) is a method used to build up a three-dimensional image of an object. This works by taking an X-ray from different positions and angles. This can be used to locate fractures in bones.
• X-rays are a form of radiation used in radiotherapy, they have a much higher energy than those used for diagnosis.

# Ultrasound

• Sounds with a higher frequency than 20000 Hz are known as ultrasounds, humans cannot hear sounds above this frequency (20-20000Hz). Ultrasounds have a longitudinal wave.
• Bats and dolphins use ultrasound waves to detect obstacles around it, the sound is reflected and the animal detect the echo.
• Ultrasound can also be used to make images of structures inside the body; an ultrasound machine ...