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AS ocr unit 2 Def.
AS ocr unit 2 Definitions.
| Question | Answer |
|---|---|
| Absorption spectra | A spectrum produced by light passing through a gas, which has dark lines where the gas has absorbed light, characteristic of the elements in the gas. |
| Amplitude | is the maximum displacement from the centre of an oscillation |
| Diffraction | The spreading out of waves when they pass through an opening or round an obstacle (into regions where they would not be expected if light travels only in straight lines) |
| displacement | How far and in what direction the body is from its equilibrium position |
| Electromagnetic spectrum | gamma 10-13-10-15 m 2,Xrays 10-8-10-13 m 5,Ultraviolet 4x10-7-10-8m 1,Visible 3.9 x10-7-7.8x10-7 m 0,Infrared 7.9x10-7-10-3m, 4Microwave 10-3-10-1m 2,Radio 10-1-105m 4 |
| Excited | Atom with one or more electrons raised above their ground state positions |
| Excitation energy | Energy require to raise an electron to a position above its ground state |
| Electronvolt | Energy transferred to an electron when it is accelerated through a potential of 1V: equivalent to 1.6 x10-19 J |
| Emission spectra | A line spectrum emitted by a hot gas which is characteristic of the elements it contains. (Coloured lines on a black background) |
| Electromagnetic wave | Transverse combination of oscillating in phase electric and magnetic fields. |
| Energy flux/ intensity | Energy that a wave carries perpendicularly through unit area each second. |
| Equilibrium position | Where resultant force on the oscillating body is zero |
| Frequency | The number of oscillations completed per second |
| Ground state | Atom with its electrons in their lowest energy positions |
| Interference | In a region where wave trains from coherent sources cross, superposition occurs giving reinforcement of the waves at some points and cancellation at others (constructive or destructive interference). |
| Ionisation | When an electron is completely freed from an atom leaving behind a positive ion. |
| Ionisation energy | Energy required to free an electron from the ground state of an atom. |
| Longitudinal waves | A wave where the displacements are parallel to the direction of propagation |
| Natural Frequency | The frequency at which a free standing system oscillates after it has been displaced and then released |
| Nodes | A point on a stationary wave where the displacement is always zero |
| Out of phase | Completely out of step with each other, π or 180 degrees. |
| Period | The periodic time is the time taken to make one complete oscillation/ rotation |
| In Phase | Two points which are in phase have a complete number of oscillations between them. |
| Phase difference | between two points in an oscillation is a measure of what fraction of a complete oscillation has been completed between the two points |
| Photon | Small packet of light energy |
| Photoelectric effect | Emission of electrons from a surface when illuminated with electromagnetic radiation of equal frequency or greater than the threshold frequency |
| Plane polarization | Vibrations are confined to a single plane perpendicular to the direction of energy propagation |
| Principle of Superposition | Where waves cross the total displacement is the vector sum of the individual displacements due to each wave at that point. |
| Progressive waves | A disturbance that does transfer energy |
| Quantum | Small packet of energy |
| Saturation | When all the emitted electrons are received by the other electrode and the maximum current flows. |
| Stationary waves | A disturbance that does not transfer energy although it does have energy associated with it. |
| Stopping potential/ voltage | Voltage across a photocell that is just sufficient to stop photoelectrons with the maximum amount of KE reaching the receiving electrode. |
| Threshold frequency | Minimum frequency that will cause photoemission from a material |
| Transverse waves | A wave where the displacements are perpendicular to the direction of propagation |
| Velocity | Rate of change of displacement |
| Unpolarised | Vibrations occur in a large number of planes perpendicular to the direction to energy propagation. |
| Wavefront | Line joining all points across adjacent rays that have exactly the same phase |
| Wavelength | The distance between two consecutive points on a wave that are in phase |
| Work function | Minimum amount of energy needed to release an electron from the surface of a metal |
| Charge | A coulomb is the amount of charge that flows when there is a current of one ampere for one second. Symbol Q.1C is the charge carried by 6.25 x 1018 electrons.Measured by a coulombmeter. |
| Current | Electric current as rate of flow of charge. |
| Law of conservation of charge | No charge is lost in a circuit or at any junction in a circuit.This is a consequent of Kirchoff’s first law. |
| Kirchoffs First law | Sum of the current entering a junction = sum of the currents leaving a junction |
| Drift speed | The average speed at which charge moves around a circuit . Typical drift velocity =10-5m/s. |
| Electrical potential difference | Potential difference or voltage between two is the work done per unit charge travelling between the two points.P.d. = work done/ charge or Potential difference (voltage) as power/current |
| Emf of a cell | Work done /unit charge in pushing the current round the whole circuit (including the internal resistance) |
| Electrical working (Work done) | Work done = Energy transfer.(This is when charge is pushed) |
| Resistance | Resistors oppose the flow of current.Resistance = voltage / current |
| Resistivity | You must write out the eqn Resitivity = resistance x cross sectional area/ length .It is a constant for a particular material of a wire. |
| Power dissipation | Power is the rate of working. Power is the rate of energy transfer. |
| Antinodes | A point on a stationary wave that oscillates with the maximum amplitude |
| Coherence | If sources of wave are coherent there must be a constant phase difference between them and therefore they must have the same frequency. They must have also approximately the same amplitude |
| Continuous spectrum | This is emitted by hot solids, hot liquids and hot gases at high pressures. All wavelengths are emitted. |
| cycle | A complete movement of an oscillating or cycle |
| De broglie wavelength | Electrons have a wavelength associated with them with is dependent on the momentum of the particle |
| Conservation of energy in circuits | Circuit e.m.f. = ΣIR.This come from Kirchoff’s second law-Around any closed loop, the sum of the e.m.f.s is equal to the sum of the p.d.s. |
| Internal resistance | This is the resistance to the flow of current inside the power supply itself. |
| Series circuits | The current passes through one component , then through the next and then through the next. The current is the same at all points in the circuit. The voltage is split between the components VT = V1 +V2 |
| Parallel circuits | The current from the cell splits at a junction. IT =I1 +I2.The current travels through branches. The voltage is the same across each branch. |
| Thermistor | This sensor changes resistance with temperature. The higher the temperature the lower the resistance. |
| Light dependent resistor | This sensor changes resistance with the level of illumination.The greater the light level the lower the resistance. |
| Ohm’s Law | The current flowing through a metal is directly proportional to the potential difference across it providing the temperature remains constant. |
Created by:
Susan E Casey
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