P5 d-f OCR gateway GCSE

P5 d-f OCR gateway GCSE

1. D

   • When two objects interact, they exert an equal and opposite force on each other. (Turn the names around to check you have the right forces!)
   • The downwards force on a boy due to gravitational attraction from Earth is equal and opposite to the upwards force on Earth due to the gravitational attraction from the
   • If no external forces act, the total momentum before a collision is the same as the total momentum after a collision (conservation).
   • Particles in a gas move randomly.
   • Pressure in gases is caused by particles colliding with each other and the walls of the container.
   • Smaller volume or higher temperature increase the pressure as the particles hit the container more frequently.
   • Pressure = force/area
   • A rocket pushes hot gas downwards, so the gas pushes the rocket upwards.

2. E

   • The highest frequency radio waves are microwaves. They are next to each other in the EM spectrum
   • High frequency waves are used to send signals to Geostationary satellites as they can penetrate the Earth’s atmosphere. Low frequency can be used for low orbit satellites.
   • Microwave signals are sent from a transmitter, then received and amplified by the satellite. Then the signal is retransmitted to Earth and picked up by a receiver.
   • The ionosphere is a layer of charged particles, high in the atmosphere.
   • Microwaves between frequencies of 3GHz and 30GHz are used for satellite communication
   • Below 3GHz, the waves are reflected from the ionosphere
   • Above 30GHz the waves are scattered and absorbed by the atmosphere.
   • Long wavelength radiowaves diffract around hills, so have a longer range.

3. F

   • Constructive interference: waves add together to give a larger wave;peak+peak or trough + trough; waves are in phase.
   • Destructive interference: waves subtract to give calm water/dark area; peak + trough; waves antiphase.
   • Lasers are used to show interference, as they are coherent (waves in phase), with same wavelength /frequency.
   • Path difference is an even number of half-wavelengths in constructive interference, and odd number of half- wavelengths in destructive interference
   • Polarised light has oscillations only in one plane.