OCR Physics - P5 Space for reflection

• GPS.

• Communications.

• Military uses.

• Scientific research.

• Weather forecasting.

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

• Orbital Period speed =  Distance from earth

• Anything with mass exerts a force of gravity. 

• The greater the mass the greater the force.

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

• It orbits the earth every 24 hours. 

Low Polar Orbit: 

• Weather forecasting.

• Mapping the earth.

High Geostationary Orbit:

• Weather forecasting.

• Communications.

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

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

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

Vector:

• Velocity

• Acceleration

• Momentum 

• Friction 

Scalar:

• Volume

• Mass

• Density

• Speed

• Area

1. 

1.

http://www.ronknott.com/MEI/MechSuvatEquns.html

• An amplification gives a signal more energy.

• 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.

• This is the number of oscillations per second.

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

• 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: 

• 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.

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

• 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. 

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. 

• 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. 

• Refraction is:

• 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.

• 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.

• Fiber optics work due to cladding.

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

• 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.  

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

• Concave lenses cause light to diverge and spread out.