3.1 Electric Quantities

Question 1

What units is charge measured in?

Answer 1

Coulombs (C)

Question 2

How much charge is there on a single electron?

Answer 2

-1.6x10^-19

Question 3

How many electrons are needed to have 1 Coulomb of charge?

Answer 3

6.25x10^18

Question 4

How can total charge be linked to the number of electrons?

Answer 4

Q = ne
Total Charge = number of electrons x charge of each electron

Question 5

What is the strict definition of current?

Answer 5

The rate of movement of charge

Question 6

When does electric current occur?

Answer 6

When a charged particle which is free to move experiences an electrical force

Question 7

What are electrons that form the current called?

Answer 7

Conduction electrons

Question 8

Which direction does conventional current flow?

Answer 8

Positive to Negative

Question 9

Which direction do negative electrons actually flow round a circuit?

Answer 9

Negative to Positive

Question 10

What is the SI unit for current?

Answer 10

Ampere

Question 11

I (current) =

Answer 11

Q/t
charge passing a point / time taken

Question 12

What actually is 1 amp?

Answer 12

The movement of 1 Coulomb of charge per second

Question 13

Why is V called potential difference?

Answer 13

Because it is the difference in potential energy

Question 14

How much energy will the electrons always have at the positive side of the battery?

Answer 14

0

Question 15

What is the definition of P.D?

Answer 15

Work done per unit charge

Question 16

What is the equation for P.D?

Answer 16

V = W/ Q
P.d = energy / charge

Question 17

What unit is P.D measured in?

Answer 17

Volts

Question 18

What is the unit for P.D?

Answer 18

Volt

Question 19

What is Electromotive Force (EMF) a measure of?

Answer 19

How much energy each electron receives as it passes though the cell/battery

Question 20

Define resistance?

Answer 20

The opposition to the flow of current in a circuit

Question 21

What is resistance measured in?

Answer 21

Ohms

Question 22

What is the equation for resistance?

Answer 22

R = V / I
resistance = P.d / Current

Question 23

What is Ohms law?

Answer 23

The current through a resistor AT A CONSTANT TEMPERATURE is directly proportional to the p.d across the resistor

Question 24

What does an I-V graph of a bulb look like?

Answer 24

A curving S shape that goes through the origin

Question 25

What does an I-V graph of a resistor look like?

Answer 25

A straight line
y=x

Question 26

What does an I-V graph of a diode look like?

Answer 26

Flat along the y axis when it is negative, but a steep incline when it is positive

Question 27

What is resistivity a measure of?

Answer 27

A measure of how much a material resists an electrical current from flowing through it

Question 28

What is the equation for resistivity?

Answer 28

rho = RA / l

Resistivity = Resistance x Area / Length of wire

Question 29

What is resistivity measured in?

Answer 29

Ohm-metres

Question 30

What is Kirchoff’s first law?

Answer 30

The sum of current entering a junction is always equal to the sum of current leaving it

Question 31

What is Kirchoff’s Second Law?

Answer 31

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

Question 32

How do you calculate total resistance in series circuits?

Answer 32

Rt = R1+R2+R3…

Question 33

How do you calculate the total resistance in parallel circuits?

Answer 33

1/Rt = 1/R1 + 1/R2 ……

Question 34

What are potential divider circuits?

Answer 34

Circuits that divide the potential difference across multiple resistors

Question 35

What is the potential divider equation?

Answer 35

Vout = Vin x R1/R1+R2