3.1 Electric Quantities Flashcards
What units is charge measured in?
Coulombs (C)
How much charge is there on a single electron?
-1.6x10^-19
How many electrons are needed to have 1 Coulomb of charge?
6.25x10^18
How can total charge be linked to the number of electrons?
Q = ne
Total Charge = number of electrons x charge of each electron
What is the strict definition of current?
The rate of movement of charge
When does electric current occur?
When a charged particle which is free to move experiences an electrical force
What are electrons that form the current called?
Conduction electrons
Which direction does conventional current flow?
Positive to Negative
Which direction do negative electrons actually flow round a circuit?
Negative to Positive
What is the SI unit for current?
Ampere
I (current) =
Q/t
charge passing a point / time taken
What actually is 1 amp?
The movement of 1 Coulomb of charge per second
Why is V called potential difference?
Because it is the difference in potential energy
How much energy will the electrons always have at the positive side of the battery?
0
What is the definition of P.D?
Work done per unit charge
What is the equation for P.D?
V = W/ Q
P.d = energy / charge
What unit is P.D measured in?
Volts
What is the unit for P.D?
Volt
What is Electromotive Force (EMF) a measure of?
How much energy each electron receives as it passes though the cell/battery
Define resistance?
The opposition to the flow of current in a circuit
What is resistance measured in?
Ohms
What is the equation for resistance?
R = V / I
resistance = P.d / Current
What is Ohms law?
The current through a resistor AT A CONSTANT TEMPERATURE is directly proportional to the p.d across the resistor
What does an I-V graph of a bulb look like?
A curving S shape that goes through the origin
What does an I-V graph of a resistor look like?
A straight line
y=x
What does an I-V graph of a diode look like?
Flat along the y axis when it is negative, but a steep incline when it is positive
What is resistivity a measure of?
A measure of how much a material resists an electrical current from flowing through it
What is the equation for resistivity?
rho = RA / l
Resistivity = Resistance x Area / Length of wire
What is resistivity measured in?
Ohm-metres
What is Kirchoff’s first law?
The sum of current entering a junction is always equal to the sum of current leaving it
What is Kirchoff’s Second Law?
The EMF around a closed circuit loop is equal to the sum of the potential drops around the loop
AKA the energy it has gained from the cell is the energy lost from going around the loop
How do you calculate total resistance in series circuits?
Rt = R1+R2+R3…
How do you calculate the total resistance in parallel circuits?
1/Rt = 1/R1 + 1/R2 ……
What are potential divider circuits?
Circuits that divide the potential difference across multiple resistors
What is the potential divider equation?
Vout = Vin x R1/R1+R2
