Igcse physics

• Electric field lines show how an object with charge would be affected by the electric field around it.
• Light travels through space as electromagnetic waves, consisting of oscillating electric and magnetic fields that are perpendicular to one another and to the direction of wave propagation.
• The speed of light is the maximum possible speed at which anything can travel.
• The direction of the electric field is shown using arrows, where the arrowhead points towards positive charges or away from negative charges.
• The direction of the electric field is shown using arrows, where the arrowhead points towards positive charges or away from negative charges.
• The speed of light is constant at approximately 300 million meters per second (m/s) in all directions and does not depend on the medium through which it passes.
• The direction of the electric field is shown using arrows, where the arrowhead points towards positive charges or away from negative charges.
• • Molecules move quickly in all directions
  • Flow, completely fill their container and can be compressed
• Simple kinetic molecular model of matter:

  • Solids:
  • Molecules close together in a regular pattern
  • Strong intermolecular forces of attraction
  • Molecules vibrate but can't move about
  • Cannot flow, have fixed shape and cannot be compressed
  • Liquids:
  • Molecules close together in a random arrangement
  • Weaker intermolecular forces of attraction than solids
  • Molecules move around each other
  • Flow, take the shape of their container and cannot be compressed
  • Gases:
  • Molecules far apart in a random arrangement
  • Negligible/very weak intermolecular forces
• Brownian motion:

  • Gas molecules move rapidly and randomly due to collisions with other gas molecules
  • Massive particles may be moved by light, fast-moving molecules
• Temperature of a gas is related to the average kinetic energy of the molecules

  • Higher temperature leads to greater average kinetic energy and faster average speed of the molecules
  • Gases exert pressure on a container due to collisions between gas molecules and the wall
  • Pressure increases with temperature at a constant volume
  • Pressure decreases with volume at a constant temperature
  • For a gas at fixed mass and temperature, pressure multiplied by volume is constant (𝒑𝑽 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕)
• Evaporation:

  • Escape of molecules with higher energy from the surfaces of liquids
  • Remaining molecules have lower average kinetic energy after evaporation, cooling the liquid
  • To increase the rate of evaporation: increase temperature, increase surface area, create a draught
  • Evaporation cools a body in contact with an evaporating liquid
• Thermal expansion:

  • When heated, solids, liquids, and gases expand
  • Expansion is smallest in solids, greater in liquids, and greatest in gases
  • Applications and consequences of thermal expansion include railway tracks and liquid in a thermometer
• Thermal capacity:

  • Internal energy of a body increases as temperature rises
  • Specific heat capacity is the amount of energy required to raise the temperature of 1kg of a substance by 1℃
  • Thermal capacity is how much energy is needed to raise a body's temperature by a given amount
• Melting and boiling:

  • Melting point is the temperature at which a solid melts
  • Boiling point is the temperature at which a liquid turns into a gas
  • Condensation is when gas molecules come together to form liquid
  • Freezing is when liquid molecules slow down and arrange into a solid
• Specific latent heat:

  • Amount of energy needed to change the state of 1kg of a substance
  • Specific latent heat of fusion is for melting/freezing, and of vaporization is for boiling/condensing
  • Energy needed for a change of state goes towards making molecules more free rather than increasing kinetic energy
• Measuring Temperature:

  • Thermocouple: contains two different metals that generate a current based on temperature difference
  • Liquid-in-glass thermometer: liquid expands or contracts with temperature changes
  • Sensitivity, range, and linearity affect the accuracy of thermometers
  • Fixed points like the melting and boiling points of water are used to calibrate thermometers
• Thermal processes:

  • Conduction: transfer of thermal energy in solids and liquids
  • Convection: transfer of thermal energy in fluids by movement of molecules
  • Radiation: transfer of thermal energy by infrared radiation, does not require a medium
  • Different materials have varying abilities to conduct, convect, or radiate heat
• General wave properties:

  • Waves transfer energy without transferring matter
  • Particles oscillate about a fixed point
• Amplitude:

  • Distance from the equilibrium position to the maximum displacement
• Frequency:

  • Number of waves that pass a single point per second
• Wavelength:

  • Distance between a point on one wave and the same point on the next wave
• Speed:

  • Distance traveled by a wave each second
  • Speed is related to frequency and wavelength by: speed = frequency × wavelength
• Reflection:

  • Waves reflect off smooth, plane surfaces rather than getting absorbed
  • Angle of incidence = angle of reflection
  • Rough surfaces scatter light in all directions
  • Frequency, wavelength, and speed are all unchanged
• Wavefront:

  • A surface containing points affected in the same way by a wave at a given time such as crests or troughs
• Types of waves:

  • Transverse waves:
  • Has peaks and troughs
  • Vibrations are at right angles to the direction of travel
  • Example: light
  • Longitudinal waves:
  • Consists of compressions (particles pushed together) and rarefactions (particles moved apart)
  • Vibrations are in the same direction as the direction of travel
  • Example: sound
• Refraction:

  • The speed of a wave changes when it enters a new medium
  • If the wave enters a more optically dense medium, its speed decreases and it bends towards the normal
  • If the wave enters a less optically dense medium, its speed increases and it bends away from the normal
  • In all cases, the frequency stays the same but the wavelength changes
• Diffraction:

  • Waves spread out when they go around the sides of an obstacle or through a gap
  • The narrower the gap or the greater the wavelength, the more the diffraction
  • Frequency, wavelength, and speed are all unchanged
• Denser medium Light Reflection:

  • When light is reflected off a plane mirror, it forms an image with characteristics like being upright, same distance from the mirror as the object, same size, and virtual
• Refraction:

  • Refraction can be shown when light is passed through a glass slab at an angle to its normal
  • Refractive index relates to the speed of light in a vacuum and the speed of light in the medium
  • Snell's law relates the angle of incidence and the angle of refraction to the refractive index
• Total internal reflection:

  • Total internal reflection occurs when the angle of incidence is greater than the critical angle and the light reflects back into the medium
  • Critical angle can be related to the refractive index
• Optical fibres:

  • An optical fibre is a long thin rod of glass surrounded by cladding
  • Uses total internal reflection to transfer information by light, even when bent
  • Used in medicine and communications
• Converging lens:

  • A converging lens brings light rays together at a point called the principal focus by utilising refraction
  • Focal length is the distance between the centre of the lens and the principal focus
  • Converging lenses are used in magnifying glasses and binoculars
• Dispersion:

  • When white light is passed through a glass prism, it splits up into its constituent colours
  • The greater the wavelength, the slower the speed in glass and the greater the refractive index
• Electromagnetic spectrum:

  • Properties of electromagnetic waves: transverse waves, do not need a medium, travel with the same high speed in a vacuum
  • Uses of electromagnetic waves: radio waves, microwaves, infrared radiation, visible light, ultraviolet light, X-rays, gamma radiation
• Hazards:

  • Exposure to ultraviolet light increases the risk of skin cancer
  • X-rays and gamma rays are ionising radiation that can cause mutations leading to cancer
  • Microwaves can cause internal heating of body tissues
  • Infrared radiation can cause skin burns
• Sound Waves:

  • Sound waves are longitudinal waves created by vibrating sources
  • Medium is needed to transmit sound waves
  • Speed of sound in air, water, and steel
  • Range of audible frequencies for a healthy human ear
  • Ultrasound is used for things such as SONAR and medical imaging
• Magnetic forces are due to interactions between magnetic fields
• Magnetic materials can be magnetised by induced magnetism
• Magnetic materials are attracted to magnets and can be magnetised (e.g. iron, steel, cobalt, nickel)