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Physics Paper 2: P5 (Waves (Interference occurs when two waves overlap. …
Physics Paper 2: P5
Waves
Interference occurs when two waves overlap. They can reinforce or cancel. This results in louder and quieter areas in sound and bright and dark areas in light. The type of interference depends on the path difference between the two waves.
Total internal reflection can occur when light goes from a dense to a less dense medium. The critical angle is the angle of incidence for which the angle of refraction is 90 degrees. At greater angles of incidence all the light is totally internally reflected. This happens in an optical fibre.
A convex lens makes a beam of light converge. Convex lenses are used in cameras and projectors to produce real, inverted images, and as a magnifying glass to produce a virtual image that is the right way up
Refraction occurs when light passes from one medium to another. As the speed of the light changes, Its direction can change.The refractive index tells us about the amount of bending
Light travels in straight lines. Diffraction and interference of light can only be explained by a wave model. Polarised light has oscillations in one plane only.
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Scalars and vectors
Changes in temperature and volume cause changes in pressure. Rate of change of momentum creates a force on the walls of the container. Rockets expel a large number of particles at high speed.
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Projectiles: Have a constant horizontal velocity, have a trajectory that is parabolic, accelerate towards the ground at 10 m/s2.
A scalar quantity (e.g. speed) has size only. A vector quantity (e.g. velocity) has size and direction. Vector diagrams are used to calculate the resultant forces.
Satellites and gravity
A gravitational force keeps a satellite in orbit. The height and period of a satellite's orbit depends on its job.
Geostationary satellites take exactly 24 hours to orbit Earth, above the equator. This means they always stay above the same point on Earth.
Any object moving in a circle needs a force towards the centre of the circle to maintain its circular path. This is called a centripetal force.
Satellite communication
Some radio waves are reflected by the ionosphere. High frequency radio waves (microwaves) pass through it to reach an orbiting satellite. Long wavelength radio waves are easily diffracted around hills: short wavelength microwaves only diffract a small amount. The amount of diffraction depends on the size of the gap or obstacle.