Unit 2 definitions Flashcards
Amplitude:
the maximum displacement from the mean position
Frequency:
the number of complete oscillations per second
Period:
the time taken for one complete oscillation
Wavelength:
the distance between the same point on two successive waves
Longitudinal waves:
direction of oscillation is parallel to the direction of propagation. Wave travels with series compressions and rarefactions.
Jan 2010: Describe how sound waves travel through air (3)
Sound waves are longitudinal (1)
Air molecules vibrate (1)
Parallel to the direction of travel of the wave (1)
In a series of compressions and rarefactions (1)
Transverse waves:
direction of oscillation is perpendicular to the direction of propagation with peaks and troughs.
Wavefront:
a line representing all points of a wave that are in phase, i.e. peaks of a wave as viewed from above.
Coherent:
Waves of constant phase relationship (Jan 2010)
Path Difference:
the difference in distance from each source to a particular point
Superposition:
when two or more waves of the same type meet at a point the resultant displacement of the oscillations will be the vector sum of the individual displacements
Phase:
Phase:
Standing Wave:
no net transfer of energy or pattern of nodes and antinodes or points of maximum displacement and zero displacement (Jan 2010)
June 2009: Explain why the amplitude of sound varies for a microphone being moved between a speaker and a screen (4)
Interference pattern produced / superposition occurs / standing wave formed (1)
Maxima related to constructive interference / antinode and/or minima related to destructive interference/node (1)
Maxima/antinode formed where the waves are in phase / path difference nλ (1)
Minima/node formed where the waves are in antiphase/path difference = (n+1/2)λ (1)
Progressive Wave:
a wave which transfers energy but not matter
Refractive Index:
the ratio of the speed of light in the two media. Absolute refractive index is the ratio of the speed of light in the medium to the speed of light in a vacuum.
Critical Angle:
The angle of incidence for which the angle of refraction is 90˚. Total internal reflection occurs beyond the critical angle.
Plane Polarised Light:
Electric & magnetic field oscillations which occur in
EITHER
one direction only which is perpendicular to direction of propagation/travel
OR
one plane only which includes direction of propagation/travel
Jan 2010: State the difference between plane-polarised and unpolarised light (1):
Unpolarised light oscillates/vibrates in many planes/directions while polarised oscillates/vibrates in one plane/direction only
Jan 2010: State why sound waves cannot be polarised (1):
Sound is a longitudinal wave or oscillations in one direction already
Diffraction:
Diffraction is the spreading out of a wave as it passes through an aperture/around an obstacle.
Doppler effect:
June 2009:
a)Describe and explain how the movement of the ambulance causes the frequency of the sound he hears to change (3)
b)Suggest how what he hears would be different if the ambulance were moving faster (2)
a)Ambulance moving towards: higher frequency/pitch (1) wavelength shorter/waves bunch together (1)
Ambulance moving away: lower frequency/pitch (1) wavelength increased/waves spread out (1)
b)For both marks reference must be made to the change in frequency being greater or range of frequencies greater
Electric Current:
the rate of flow of charged particles
Resistance:
defined by R=V/I where Ohm’s Law is a special case when I∝V
Jan 2010: State Ohm’s Law (2):
Current through a conductor is directly proportional to the potential difference across it (1)
providing the temperature of conductor remains constant (1)
e.m.f.:
the electrical energy per coulomb supplied to a circuit by the cell
potential difference:
the electrical energy per unit charge transferred to other forms
Jan 2009: Explain, in terms of energy, the difference between potential difference (p.d.) and electromotive force (2)
p. d. is electrical energy per coulomb transferred between two points / electrical energy transformed / converted to other forms (1)
e. m.f. is the energy per coulomb supplied to a circuit/given to the charge/energy output of the cell (1)
drift velocity:
Average velocity of charge carriers in a conductor
Semiconductors:
Jan 2010: State and explain what happens to the resistance of a sample of silicon as its temperature increases (2)
Resistance decreases (1) because as temperature increases n increases (/ there are more electrons / charge carriers) (1)
Threshold frequency:
the frequency of light just large enough to liberate electrons
Work function:
the minimum energy required to just remove an electron from the surface of a metal.
Radiation Flux:
power per unit area
Energy Level:
Allowed energy of an atom or electron in an atom
Photon:
a photon is a discrete package/packet/quantum of electromagnetic energy/light
June 2009: What is an energy level? (1)
Allowed/possible energy of atom/electron (in an atom)
Discrete energy of an atom/electron
One of the energies of the atom/electron
Energy an atom/electron can have
Jan 2010: Explain how Einstein’s results for his work on the photoelectric effect support a particle theory, not a wave theory of light (6)
Particle Theory (max 4 marks):
Reference to E=hf or quanta of energy / packets of energy / photons (1)
Increased f means more energy of a photon (1)
Release of electron requires minimum energy / work function (1)
One photon releases one electron (1)
Greater energy of photon means greater KE of electrons (1)
More intense light means more photons, therefore more electrons (1)
Wave theory (max 2 marks): Wave energy depends on intensity (1) More intense light should give greater KE of electrons (1) Energy is spread over the whole wave (1) If exposed for long enough photons eventually released, this doesn’t happen (1)
June 2013: Explain why the following observations may be understood by using a photon model of light, rather than a wave model. (5)
• Light above a certain frequency causes the emission of electrons from the
surface of a metal. This emission occurs instantaneously.
• Light below a certain frequency will not result in the emission of electrons
however long it illuminates the surface.
describe relevant interaction between single photon and single electron (1)
photon energy depends on frequency Or reference to E = hf (must be link to photons/light) (1)
if photon energy greater than work function, electron emitted (immediately) (1)
whereas for waves energy could build up Or with waves that the electron can absorb energy continuously or over time (1)
so any frequency should work Or but this build up doesn’t happen (1)
