Module 4 paper 2 Flashcards
Define current
rate of flow of charge
define 1 coulumb
the flow of carhe in a time of 1 second when the current is 1 ampere
how is a current produced in a metal
In a metal, there is a lattice of positive ions, surrounded by free electrons. The
positive metal ions are fixed in place, but the electrons can move around, and so when one side
of the metal is made positive, and the other side is made negative, the electrons will be attracted
to the positive side, and move through the metal as electric current
how is a current produced in an electrolyte
ionic sollution, when a pair of electrodes are placed in the cations and anions split and are attracted to the electrodes producing a flow of charge
kirchhoffs first law
at any point in an electrical circuit, the sum of the currents in the junction is equal to the sum coming out that junction
define mean drift velocity
is defined as the average velocity of the electrons as they travel down the
wire, colliding with positive metal ions
define potential difference
is used to measure the work done by charge carriers, which lose
energy as they pass through the components in a circuit. It is defined as the energy transferred
from electrical energy to other forms, per unit charge
define electromotive force
used to measure the work done to charge carriers, when they gain
energy as they pass through a cell or power supply. It is defined as the energy transferred from
chemical energy to electrical energy per unit charge,
what is an electron gun and how does it work?
used to produce a thin beam of electrons, which are accelerated to
high speeds. A small metal filament, which acts as a cathode, is heated by passing a potential
difference through it. Some of the electrons in the metal gain enough kinetic energy to escape the
metal, in a process known as thermionic emission. The circuit is in a vacuum tube, with a high
p.d., V, between the filament and the anode, so the freed electrons are accelerated towards the
anode. If the anode has a small hole in it, a beam of electrons can pass through at a specific
kinetic energy.
how to calculate the velocity of an electron
ev = 1/2mv^2
define resistance
potential difference across a component divided by the current in it
ohms law
for a metallic conductor kept at a constant temperature the current in the wire is directly proportional to the potential difference across it
why does ohms law not apply to some components
when the current across the component increases, the metal ions are
heated, gaining kinetic energy and vibrate more around their fixed points in the metallic lattice.
This increases the frequency of collisions with electrons, so more work is done on the charge
carriers, increasing the resistance
current against voltage graph for component that obeys ohms law
current against voltage fraph for filament
determine resistivity
First, the
cross sectional area of the wire is recorded, by taking multiple readings with Vernier callipers at
different points along the wire, and taking an average. Then, a circuit is set up using a recorded
length of the wire, with a voltmeter connected in parallel and an ammeter in series. The values
for p.d. and current can be recorded to determine the resistance of the wire, and used along with
the length and cross sectional area to determine the resistivity of the material the wire is made
from
define electrical powert
rate of energy transfer and tis measured in watts
kirchoffs second law
in any circuit the sum of the electromotive force is equal to the sum of the potential difference in a closed loop
internal resistance and lost volts
not all of the energy transferred
to the charge carriers is available to the circuit, as some is transferred to the internal resistance of
the cell. This results in a difference between the measured p.d. across the terminals of the power
supply, and the actual e.m.f. of the cell, which is referred to as the ‘lost volts’, and is equal to the
p.d. across the internal resistor
determine internal resistance
To determine the internal resistance of a cell, the cell with internal resistance r is connected in
series to an ammeter and a variable resistor. A voltmeter is connected in parallel around the cell.
The resistance of the variable resistor is varied, and the V and I readings recorded. The equation 𝜀 = 𝑉 + 𝐼r is rearranged to 𝑉 = 𝜀 − 𝐼r. When a graph of terminal p.d. (V) against current (I) is
plotted, the y intercept of the graph will be the e.m.f. of the cell and the negative gradient will
be the internal resistance of the cell.
Potential divider circuits
From Kirchhoff’s second law, we know that in a series circuit the current is constant, and the p.d.
splits in a ratio proportional to the resistance of each component By considering the ratio of the resistance for one component with the total circuit resistance, we
can determine the potential difference across this component, using the formula
define progressive wave
an oscillation that travels transfers energy from one place to another without transferring matter
define transverse wave
wave osciallations occur perpindular to the direction of travel
define logintude wave
wave oscialltions occur perpindular to the direction of travel
define amplitude
maximum displacement from equilibrium position
phase difference
difference in displacement of particles along a wave