Terms in this set (24)
Speed, Velocity and Acceleration
speed = distance/time
acceleration = change in velocity/time
velocity = speed in a specified direction
Mass and Weight
Mass measures the amount of matter in an object
Weight is the force of gravity acting on an object
density = mass/volume
Forces and Change of Motion
Resultant force: gives an acceleration to an object. If object is stationary, it will gain speed. If object is moving, it will gain or lose speed depending on the direction of the force.
Planet in orbit: gravitational force towards sun
Car turning a corner: friction force
Ball on a length of string: string tension
Work and Power
Work is done when a force moves through a distance
The greater the force, the more work
Work done = force x distance moved in direction of force
Power is the rate of doing work
The greater the work done in a given time, the greater the power
Power = work done/time taken
Pressure on a surface is the force exerted on a given area
The greater the force on a given area, the greater the pressure
The smaller the area the given force acts upon, the greater the pressure
Pressure = force/area
Barometers are used to measure atmospheric pressure in millimetres of mercury, which is given by the height of the mercury column.
Changes of State
Boiling: occurs at a definite temperature called the boiling point. Bubbles/vapour form in the liquid and rise.
Condensation: occurs when gas or vapour molecules return to liquid state.
Melting: takes place at a definite temperature called the melting point. Energy is provided to break bonds between molecules.
Solidification: occurs when molecules of a liquid returns to solid state. This takes place at freezing point.
At a constant temp, gas molecules move at a constant average speed, so the force from each collision is the same.
Smaller volume = increase in pressure
At a constant temperature:
pressure x volume = constant
Transfer of Thermal Energy
Heat is always transferred from a place of high temp to low temp
Conduction-In conduction, heat is transferred through a material without movement of the material.
Convection-In convection, heat is transferred by a fluid due to movement of the fluid itself. The fluid expands on heating so its density falls. The warmer and lighter fluid rises to the cooler region, transferring heat in the process.
Radiation- In radiation, heat is transferred by infra-red radiation, which is a part of the electromagnetic spectrum. Most solids and liquids absorb infra-red radiation, including water which is transparent to light.
Nature of Waves
Travelling wave in which oscillation is perpendicular to direction of travel
(eg waves, earthquake, electromagnetic wave)
Travelling wave in which oscillation is parallel to direction of travel
(eg earthquake, sound)
Frequency: the number of complete cycles which occur in one second (pitch)
frequency = number of cycles/time
Wavelength: the distance between two corresponding points in a successive cycles of a wave
Amplitude: the maximum displacement of a wave from the undisturbed position (volume)
Reflection-The reflected waves are at the same angle to the reflecting surface as the incident waves. Speed, wavelength and frequency are unchanged by reflection.
Refraction- When waves enter, their speed is reduced, Their frequency stays the same so their wavelength is also reduced. the refracted waves change direction.
Diffraction- Speed, wavelength and frequency are unchanged by diffraction.
All rays of light parallel to the principal axis are refracted by the lens to pass through the principal focus. The distance between F and the optical centre, C, is called the focal length
Dispersion of light: White light is mad up of seven colours. Prism + light = rainbow (Pink Floyd album cover)
1. They can all travel through a vacuum at the same high speed.
2. They show the normal wave properties of reflection
3. They are transverse waves
4. They travel due to moving electric and magnetic fields
These rays include: Gamma rays, X-rays, Ultraviolet (UV)
-Opposite poles attract
-Magnetic field lines always go from N to S
-Magnetic materials are mostly ferrous metals, such as iron, steel and their alloys, along with Cobalt and Nickel.
-Magnetic field can be produced by a permanent magnet or a wire carrying an electric current.
-Wire or a coil carrying an electric current produces a magnetic field
-higher current = strong magnetic field
-current reverses = direction of m.f reverses
Remember: right hand grip rule, corkscrew rule
Electric Current, Electromotive force and Potential Difference
I= current Q= charge t= time
-Electric current: Flow of charge measured in amps (must be connected in series)
-Electromotive Force: source of electrical energy for a whole circuit, measured in volts
-Potential difference: is a measure of electrical energy transferred in the component, measured in volts. Voltmeter must be connected in parallel with circuit elements.
R= resistance in ohms V= Potential Difference
Greater the resistance, smaller the current
Greater the potential difference, greater the current
Motor effect, Electromagnetic Induction and Transformers
Motor Effect- refer to image
Electromagnetic Induction: when the magnetic field through a circuit changes, a voltage is induced. The induced emf (voltage) increases with the increase of:
-speed of motion of the magnet and circuit
-number of turns on the coil
-strength of magnet
-transformers only work with a.c.
power loss in a cable = p.d. across a length of cable x I (current)
p.d. = I x resistance of cable (R)
power loss = I x R x I = I2R
Alpha particles: a helium nucleus made up of two protons and two neutrons
-(stopped by thick paper)
Very high ionising power, very strong
-charge -> +2
Beta particles: a high-speed electron emitted by a nucleus
-(Stopped by a few millimetres of aluminium)
Ionising effect weak
-charge -> -1
Gamma particles: a high-frequency electromagnetic wave --(Only stopped by many centimetres of lead)
Ionising effect very weak
-charge -> none
-Occurs when an unstable nucleus decays and emits one or more of the three types of radiation
-When radioactive particles and molecules in the air collide, the radioactive particles knock electrons out of atoms leaving molecules positively charged (ionisation)
-Background radiation occurs naturally, due to radioactivity in rocks and the air due to cosmic rays.
-Radioactivity is detected by a Geiger counter
-Alpha decay: nucleus loses two neutrons and two protons. nucleon number goes down by 4.
e.g. radium-226 -> randon-222 + a particle
-Beta decay: neutron in the nucleus changes to a proton and an electron, which is emitted at high speed as a beta particle.
e.g. carbon-14 -> nitrogen-14 + b particle
-Gamma decay: gamma rays are usually given off during both alpha decay and beta decay and can be added onto the equations
e.g. carbon-14 -> nitrogen-14 + b particle +g particle
-The average time for half the atoms in a radioactive sample to decay
-There may be small fluctuations but with a large number of atoms in even a small sample, half life is effectively constant.
-If a sample of 10,000 atoms has a half-life of one hour, 5000 atoms decay in the first hour and 2500 decay in the second hour
Equations Round-Up Part Uno
speed = distance/time
density = mass/volume
acceleration = change of velocity/time
a = ^v/t
force = mass x acceleration
F = ma
work done = force x distance moved in direction of force
^W = fd
power = work done/time
pressure = force/area
kinetic energy = 1/2 x mass x velocity^2
k.e = 1/2 mv^2
potential energy = mass x acceleration due to gravity x change in height
p.e. = mgh
Equations Round-Up Part Dos
velocity = frequency x wavelength
resistance = voltage/current
R = V/I
current = charge/time
I = Q/t
energy = voltage x current x time
E = VIt
power = voltage x current
P = VI