# OCR Physics - P5 Space for reflection

B5 revison cards. Covering all B5.

Check out my other stuff, I revise by making these, so they are for all sciences as I revise.

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## Uses of artifical satellites?

• GPS.

• Communications.

• Military uses.

• Scientific research.

• Weather forecasting.

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## The lower the satellite is from the earth, the wha

• Lower orbit satalites orbit faster around the earth because the gravitational force is stronger.

• Orbital Period speed =  Distance from earth

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## What is gravity?

• Anything with mass exerts a force of gravity.

• The greater the mass the greater the force.

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## What is a geostationary satellite?

• A geostationary satellite is one which stays over a fixed point across the equator.

• It orbits the earth every 24 hours.

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## Uses for low polar/high geostationary orbit satell

Low Polar Orbit:

• Weather forecasting.

• Mapping the earth.

High Geostationary Orbit:

• Weather forecasting.

• Communications.

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## Relative speed of moving objects.

• Two objects moving in the same direction have lower relative speed.

• Two objects moving in the opposite direction have a higher relative speed.

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## Vector and Scalar quantities?

A vector has both magnitude and direction. A scalar has only magnitude.

Vector:

• Velocity

• Acceleration

• Momentum

• Friction

Scalar:

• Volume

• Mass

• Density

• Speed

• Area

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1.

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1.

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## What is amplification?

• An amplification gives a signal more energy.

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## Diffraction

• When waves meet a gap in a barrier, they carry on through the gap.

• The waves spread out into the area beyond the gap.

• The extent of spreading depends on the width of the gap compared with the wavelength of the waves.

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## What is frequency?

• This is the number of oscillations per second.

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## What is the ionosphere?

• A region of atmosphere where molecules have been ionised by sun radiation.

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## How do horizontal projectiles work?

• Horizontal motion is not affected by gravity (vertical motion)

• Horizontal motion is constant in projectiles.

• The path of a projectile is always a parabola.

Example of a parabola:

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## How to work out momentum?

• Momentum = Mass * Velocity

• Momentum (kg m/s) = Mass (kg) * Velocity (m/s)

• The greater the mass of an object the larger the momentum.

• Without external forces momentum is conserved.

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## Working out recoil?

1.  Recoil m/s = mass of bullet * velocity of bullet / mass of gun

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## Working out newtons of force?

• Force acting (N) = change in momentum / time taken for change to happen

Example:

change in momentum = 100 kg m/s

time taken = 0.2 s

newtons of force = 100 / 0.2 = 500 newtons of force

Note: this only applies when the change in momentum is constant over time.

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## What frequency waves travel which routes?

Ground Waves:

• Travel in close contact with the ground.

• Long wave/medium radio waves. (3 MHz)

Sky Waves:

• Short wave radio waves. (30 MHz)

• Travel up to the ionosphere where they reflect.

• Allows them to travel furthur distances.

• Overcomes the curvature of the earth.

Space Waves:

• Microwave signals (3000 MHz)

• Pass through the ionosphere and are reflected off satellites orbiting the earth.

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## What are transverse waves? How can they be filtere

• All electromagnetic waves are traverse.

• Transverse waves can be polarized to prevent the passing of waves from horizontal sources:

• So you can only see things from light sources you are looking at an angle.

• This reduces glare.

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• Refraction is:

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## What is refraction? Part 2

• When a wave enters a denser medium, it is slowed down and bends towards the normal.

• When a wave enters a less dense medium, it speeds up and is bent away from the normal.

• As usual, the normal is 90° from the object's surface.
• As the light enters the dense glass, it bends towards the normal.
• As the light leaves the glass to the less dense air, it bends away from the normal.
• The refracted wave is called the emergent ray.
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## Critical angle and Total internal reflection is wh

• The point after which light will be reflected, rather then refracted is called the Critical angle.

• Light which is reflected back into the glass is called a total internal reflection.

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## How do fiber optics work?

• Fiber optics work due to cladding.

• The cladding (like mirrors) do not absorb light, they only reflect it.

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## Snell's Law is what?

• Snell’s law relates the angle of refraction to the angle of incidence as a light wave enters or leaves a more optically dense material.

n = sin i/ sin r

• n is the refractive index of the more dense material such as glass, water etc.

• If you know two of either, n, r or i, then this equation can be worked out.

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## Convex and Concave lenses do what?

• Convex lenses focus light to converge towards a focal point.

• Concave lenses cause light to diverge and spread out.

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