GCSE Physics

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Explaining Motion.

  • Interaction pairs forces are equal in size but opposite in direction, they act on different objects.
  • Vehicles (and people) move by pushing back on something, causing a forward force on them.
  • Reaction force: the force created to counteract a force, e.g. the weight of a book on a table. 
  • The friction force matches the applied force that is making objects slide
  • Average speed of a moving object: distance/time taken
  • Instantaneous speed - speed at a particular instant
  • Velocity - speed in a certain direction
  • When a force acts on an object it causes a change in it's momentum
  • Momentum = mass  x  velocity 
  • Change of momentum = force  x  time 
  • Vehicle safety - the longer the impact time the smaller the av. force 
  • Work is the energy which makes an object move 
  • Amount of work = force  x  distance 
  • When something works, it's energy decreases by that amount and vice versa 
  • Doing work on an object increase it's gravitational potential energy (by liftinf it up) or it's kinetic energy (by making it move faster)
  • As GPE decreases, kinetic energy increases and alternatives
  • Change in GPE is '1/2  x  mass  velocity^2'
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Electric Circuits.

  • Electric charge cannot be created or destroyed but can be moved from one object to another.
  • An electric current is a flow of charges which are already present in the materials of the circuit. 
  • The battery makes the charges move around the circuit. 
  • Current doesn't get used up but does transfer energy from the battery to other components.
  • Voltage of a battery is measure of it's 'push' on the charges. 
  • Components in a circuit resist the flow of charge. Bigger resistance = smaller current. 
  • Together the battery, voltage and resistance detirmine the current in the circuit. 
  • Total resistance of resistors in parallel is less than that of any single resistor - the group provides more loops for charges to flow around. 
  • A voltmeter measures the potential difference between 2 points it's connected to.
  • Resistors in parallel have the same p.d. across each of them.
  • P.d. across resistors in series is proportonial to their resistance. 
  • The power (energy/sec) transferred by an electric circuit is equal to 'current  x  voltage'.
  • A p.d. is induced across the ends of a wire/coil placed in a changing magnetic field.
  • Electromagnetic induction (transformer coursework)
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The Wave Model of Radiation. Part 1.

  • A wave is disturbance moving through a medium. The particles move but the medium doesn't move as a whole in the direction of the wave. 
  • A wave carries energy and information through the medium. 
  • The amplitude of a wave is the maximum disturbance of each particle of the medium as the wave passes.
  • The frequency is the number of waves produced/second by the source.
  • The wave speed is the speed at which each wave crest moves through the medium. 
  • Amplitude and frequency depend on the source, wave speed depends on the medium. 
  • Wave speed = frequency  x  wavelength
  • The bigger the frequency the smaller the wavelength.
  • Reflection - wave hits a barrier and bounces back off it. 
  • Refraction - waves change their wavelength if they travel from one medium to another in which their speed is different. 
  • Diffraction - like Pink Floyd album cover.
  • Interference - when two waves meet. If waves have the same frequency, an interference pattern is formed. In some places crests add to crests, forming bigger crests; in other places crests and troughs cancel each other out. 
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The Wave Model of Radiation. Part 2.

  • Light behaves like a wave, showing diffraction and interference. 
  • The electromagnetic 'family' of waves all travel through a vacuum at 300,000km/s.
  • Electromagnetic waves have different properties based on their frequency.
  • Radio, microwave, infrared, visible light, ultra violet, x-rays, gamma rays.
  • UV, x-rays and gamma rays are ionising - they can cause chemical changes in materials that absorb them.
  • Electromagnetic waves can be used to carry information. This is 'coded' on to a carrier waves, as changes in amplitude or frequency (analogue signals), or by pulsing the beam on and off very rapidly (digital signals). 
  • Digital signals can be communicated more accurately, with less unwanted noise. 
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