ELECTRICITY Flashcards
(39 cards)
What is Plasma?
An ionised gas that has had its molecules provided with enough energy to allow ions and electrons t co-exist.
What is resistance?
Resistance is the opposition to the flow of charge. This is because of the electrons colliding with the ions within the wire causing them to lose energy. It can be described as how hard it is for the charge carriers to pass through a wire.
What is Ohms Law?
The current in an ohmic conductor is proportional to the voltage across it, provided that the temperature and other physical conditions are kept constant.
What is drift velocity
The average velocity of electrons as they move from negative to positive since electrons move randomly. It is much slower than the actual speed of electrons because it is the average velocity.
Derive drip velocity equation
I=Q/t
Q= Ix t
D= s x t
s= v x t
n = number of electrons
Q= n x q
Q= v x n x q
V= A x l
Q = A x l x n x q
l is the distance so
Q= A x v x t x n x q
Q/t = …
I= n x v x A x q
What is Kirchhoff second law
In any complete loop within a circuit, the sum of all voltages across components which supply electrical energy (such as cells or generators) must equal the sum of all voltages across the components in the same loop.
Kirchhoff first law
The sum of the current leaving any junction is always equal to the sum of the currents that entered it at the same rate.
What happens to resistance in wires as temperature increases?
The higher the temperature, the greater the metal atoms oscillate, and the more frequent the collisions between electrons and lattice ions, increasing resistance.
What is resistivity?
It describes the extent to which a material opposes the flow of electric current through it. The greater the resistivity, the greater the resistance.
How does length affect resisitivity
The longer the wire the more atoms there are in the metal lattice which means there will be more collisions as the electrons drift through the metal and thus an increase in resistance.
How does cross sectional area affect resistivity
The greater the cross sectional area of a wire the more space there is between ions in the metal lattice. This will result in less collisions between the electrons and metal ions therefore a decrease in resistance.
Material of the wire on resistivity
The more tightly an atom holds on to its outermost electron the harder it will be to make a current flow. The electronic configuration of an atom determined how willing an atom will be to allow an electron to leave and wander through the lattice. Metals inherit resistivity.
Proportionalities of resistance
Length is proportional to resistance
Resistance is inversely proportional to area
Resistance is proportional to resistivity.
Practical for measuring resistivity
Get one metre of wire. Measure voltage and current every 10cms. Calculate the resistance every 10cms. Plot length of wire vs resistance on a graph. Gradient= P/A
What is EMF
Defined as the electrical energy supplied to the circuit per unit charge. E= W/Q
What is the difference between Voltage P.D and EMF
Voltage= the energy that is transferred to the components.
EMF- the energy transferred to the electrons.
P.D - the difference in energy between two points in a circuit which depends on resistance.
What is internal resistance?
The oppositions to the flow of current by the cells and batteries themselves resulting in the generation of heat.
The resistance of the materials within the battery. It is internal resistance that causes the charge circulating to dissipate some electrical energy from the power supply itself. This is why the cell becomes warm after a period of time.
EMF = TERMINAL PD + LOST VOLTS
What does v being less than the emf tell us
Not all of the emf is being transferred to the circuit and voltage has been lost
How to derive EMF
EMF = TERMINAL PD +LOST VOLTS
E= V+v
V= IR
E= IR+Ir
E= I (R+r)
E= V+Ir
V= E-IR
(E is the y intercept and -IR is the negative gradient.
Explain how a voltmeter reading will change if placed across a thermistor if temperature increases?
Increasing the temperature in a thermistor:
increases the number of free CHARGE CARRIERS (electrons)
so it’s RESISTANCE decreases
This causes the CURRENT in the thermistor to increase,
so the P.D. across the thermistor will decrease
Explain why connecting the voltmeter across both the ammeter and the thermistor would improve the experiment.
Current flows through the voltmeter but in the new arrangement it would only read the current going through the thermistor.
A NTC was used in this circuit. With reference to charge carriers in the thermistor, explain what happens to the pd across the thermistor as the temperature increases.
As temperature increases the number of free charge carriers increases so resistance will decrease.
Thermistor resistance as a proportion of total resistance decreases so the current increases so pd across resistor increases.
PD across thermistor decreases.
What are potential dividers
Potential dividers are circuits which produce an output voltage as a fraction of its input voltage
What happens in the output voltage if the temperature increases on resistor one
Temperature increases
Thermistor resistance decreases.
Voltage of thermistor decreases.
Output voltage to increases.
