Module 4 Flashcards
what is the definition of current in
* metals
* electrolytes
- metals: flow of electrons
- electrolytes: flow of ions
what is the ‘number density’?
the number of free charge carriers per unit of volume
what is drift velocity?
the average velocity of the charges moving along a conductor
not uniform journey as collides with positive metal ions
explain the term mean drift velocity of electrons in a metal wire
- free electrons make collisions with metal ions to give them a random velocity
- the free electrons drift towards the positive end the supply along the wire
- the distance travelled per unit time along the length of wire is called the mean drift velocity of the electrons
define the electro motive force
- measures the work done to charge carriers when they gain energy at the power supply
- energy transfered from chemical–> electrical
ε = W/Q where ε = electromotive force (in Volts), W = work done (in Joules) and Q = charge (in Coulombs)
the output
what is the difference between the emf and p.d?
- emf: charges gain energy
- pd: charges loose energy
- emf: chemical energy turns electrical
- pd: electrical energy to heat/ other forms
- emf and p.d work done by charges (Volts)
what is ohms law?
which temperature of a (ohmic) comductor is constant, the current is directly proportional to the p.d
r is constant
draw IV graph for resistor
draw an IV graph for a filament light bulb
draw an IV graph for a diode/LED
PAG 3- techniques and procedures used to investigate elctrical charactertistics
Describe the practical on how to measure the resistivity of a wire
how would you measure emf and terminal voltage?
- emf: voltmeter in parallel with battery unconnected to rest of circuit
- terminal volatge: in parallel with battery connected to rest of circuit
how would you determine r?
- record values of terminal voltage with varying current
- plot graph
- gradient =-r
- y intercept = ε
Why happens to V out as the contact is moved towards A and B?
As moves towards A, V out increases until = V in
As moves towards B, V in decreases until =0
what is reflection?
when a wave changes direction at a boundary between two media, remaining in the original medium
* wavelength, frequnecy do not change
what is refracation?
when a wave changes speed as it changes direction at the boundary of two media
* frequnecy the same
* wavespeed and wavelength change
will always be partial reflection
what is diffraction?
the spreading out of a wave front as it passes through a gap
* hyeogens principle: when a wave is disturbed each point where there is a disturbance becomes a source for a spherical wave
maximim difraction when gap is same size as incident wavelength
what is polarisation?
- a property of transverse waves
- particles oscillate in one direction only
what is the plane of polarisation of an EM wave?
the plane in which the electric field vibrates
what is relationship between intensity and amplitude?
intensity= (amplitude)^2
what are the techniques and procedures used to demonstrate wave effects using a ripple tank?
to show diffraction- create water waves in the tank and vary the size of the gap they pass through
