# Physics Unit 3 Edexcel

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• Created by: Katie
• Created on: 19-10-16 21:49
Intensity (W/m²) = Power (w) x Area (m²)
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What happens when distance from radioactive source increases?
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What does short-sighted mean?
You can focus on near objects but not distant ones.
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What does long-sighted mean?
You can focus on distant objects but not near ones.
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What type of lens is used to correct short-sightedness?
Diverging lens as it brings rays together further away so its focused on the retina.
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What type of lens is used to correct long-sightedness?
Converging lens as it brings rays together at the retina.
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Power of a lens
Power (Dioptres, D) = 1 / Focal Length (Metres)
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Position of an image
1/f = 1/u + 1/v (F=focal length, U=object distance, V=image distance)
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Law of Refraction (Snell's Law)
N = Sin i/ Sin r (i=angle of incidence, r=angle of refraction/reflection)
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What is refraction?
A change in the direction of a light ray that happens when it changes from one medium to another.
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What do rays of light that meet at 90 degrees do?
Continue into the material without a change of direction.
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What are Endoscopes used for and what do they make use of?
To look inside a body and allow key-hole surgery. They use optical fibres.
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What is Ultrasound?
A sound with a frequency above 20,000 Hertz that can travel through tissue without causing any damage. The sound is reflected when theres a change in speed of the waves.
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Current in X-Ray tubes
Current (Amps) = Number of particles (1/s) x Charge carried by each electron (Coulomb)
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What is the charge of an electron?
1.6 x 10 (−19) Coulombs
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Kinetic Energy
Kinetic Energy (joules, j) = 1/2 Mass of Electron (kg) x Velocity of electron (m/s) squared
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Critical Angle
Sin C = 1/n (Refractive Index)
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## Other cards in this set

### Card 2

#### Front

What happens when distance from radioactive source increases?

### Card 3

#### Front

What does short-sighted mean?

### Card 4

#### Front

What does long-sighted mean?

### Card 5

#### Front

What type of lens is used to correct short-sightedness?