4.1 Electricuty Flashcards
Electric current is the rate of flow of charge what is the equation for that
I = change in charge ( Q ) / Change in time (T)
What is conventional current
Current flows from positive to negative terminal
What is electron flow
In reality electrons flow from negative to positive terminal
What is kirchoff’s first law
The sum of current in and out of a junction algebraically are the same
What is electric current and what is the equation
The rate of flow of charge
Current= change in charge/ change in time
What does e.m.f stand for and what is is
electromotive force.
It is the chemical energy to electrical energy per unit charge
What does p.d stand for and what is it’s definition
Potential difference and it is the electrical energy to other forms of energy
How to calculate the e.m.f
E.m.f = energy transferred/ charge
NEVER BACK DOWN NEVER WHAT???
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Draw the I-V graph for a lamp
[draw it]
Draw the I-V graph for a diode
[draw it]
What is resistivity
And objects opposition to the flow of charge
What is the equation for resistivity
Resistivity = resistance X area / length
what is the rule for current in a series circuit
series circuit, the current is the same for all components
what is the rule for p.d in series circuit
p.d is shared between all components
what is the rule for resistance in series circuit
total resistance is the sum of all resistances
what is the rule for p.d in parallel circuit
p.d for cell/battery is the p.d for each branch
what is the rule for current in parallel circuits
the current is split between the branches
what is the rule for resistance in parallel circuits
The sum of the resistance in parallel circuits is equal to the sum of the inverse of each individual resistances
1/Rt= 1/R1 + 1/R2 + 1/R3
what is resistance
the opposition to current
What is drift velocity
The net movement of electrons
Resistance =
Potential difference/current
Kirchhoff’s second law
The sum of the e.m.f is equal to the sum of the potential difference in series
What is potential difference
The work done per unit charge
What is one coulomb
The amount of charge that passes in 1 second when the current is 1 amp
Energy transferred electricity equations
W=VQ
Define potential difference of 1 volt
1 joule of energy transferred per coulomb
What is the mean drift velocity
The average velocity of the charge carriers
What is the mean drift velocity equation
I = Anev
Current = Cross sectional area x number density of electrons x size of charge in one electron x mean drift velocity’s
Equation for resistance is
R= V/I
What 3 things does resistance depend on?
-Length(L) the longer the wire the more difficult it is for current to flow
-Area (A) the wider the wire the easier it will be for electrons to pass through
-Resistivity (ρ) depends on material wire is made from how easy electrons flow through a material
Resistivity definition and unit
The resistance of a 1m length with a 1m^2 cross-sectional area
-Ohmmeters is unit
What is ohms law
If the temperature is constant the current through an ohmic conductor is directly proportional to the potential difference
Why is the I-V characteristic for a metallic conductor a straight line
-At a constant temperature the current is directly proportional to the potential difference
- metallic conductors are ohmic- they have constant resistance just so long as the temperature doesn’t change
Why is it characteristic for lamp curved
Current flowing though lamp increases its temperature. So the resistance increases
Why does the resistance of a metal increase with temperature
Heating makes it harder for electrons to move about. The ions vibrate more when heated so the electrons collide with them more often. Ionising energy gets lost to other forms
Why do semi conductors resistance decrease as the potential difference increases
Semi conductors have higher resistance because there are fewer charge carriers available.
If energy is supplied more charge carriers are released so resistivity decreases.
So they are good for detecting changes
Power definition
Power is the rate of transfer of energy or one joule of work done per second
Formula for power in electrical circuits
P=IV
Give equation 2 for power
Power = (Voltage)^2 / Resistance
P= I^2 R
Give Equation 3 for power
Power = (Current)^2 X Resistance
An equation for power that links work done and time
P= W ÷ t
Power = work done ÷ time
Explain how voltage is affected when temperatures change for thermistors
componentAs temperature of thermistor increases, resistance of thermistor decreases
Total resistance of circuit decreases and current increases
Greater proportion of p.d. across fixed resistor
Reading on the voltmeter will increase
Copper is a metal, carbon is a semiconductor and ceramic is an insulator.
Describe the difference between these three materials in terms of the number density n free electrons. Include an explanation of the term number density.
n = number of (free) charge carriers per unit volume
The larger the value of n, the better the conduction
Copper has a larger n than carbon which has a larger n than ceramic
