Electric Circuits

Question 1

Charge Definition

Answer 1

The property of the protons and electrons within an atom which experience a force within the electric field.

Question 2

What is the charge of a single electron?

Answer 2

1.60 x 10^-19 C

Question 3

What is charge measured in?

Answer 3

Coulombs / C

Question 4

Charge in a series circuit….

Answer 4

is the same everywhere.

Question 5

Charge in a parallel circuit…

Answer 5

sum of charge equals total charge.

Question 6

Current Definition

Answer 6

Current is the rate of flow of charge from positive to negative terminal.

Question 7

Current Equation

Answer 7

Current = Charge / Time

Question 8

What is the Principle of Charge Conservation?

Answer 8

Total electric charge in a closed system does not change.

Question 9

What is Kirchhoff’s First Law?

Answer 9

Total current flowing into a junction is equal to current flowing out.

Question 10

What is current measured in?

Answer 10

Amps / A

Question 11

In a series circuit current…

Answer 11

is the same everywhere.

Question 12

In a parallel circuit current…

Answer 12

sum of currents equals the total current.

Question 13

Potential Difference Definition?

Answer 13

The energy transferred per unit charge between two points.

Question 14

Potential Difference Equation

Answer 14

Voltage = Energy Transferred / Charge

Question 15

Potential Difference in a series circuit…

Answer 15

the sum of all the voltages is equal to the total potential difference.

Question 16

Potential Difference in a parallel circuit…

Answer 16

potential difference is the same across each branch and sum to give total potential difference.

Question 17

The sum of all voltages in series is…

Answer 17

equal to the battery voltage or sum of all the voltages is 0

Question 18

Resistance Definition

Answer 18

A measure of how difficult it is for charge carriers to pass through a component.

Question 19

Resistance Equation

Answer 19

Resistance = Voltage / Current

Question 20

What is Ohms Law?

Answer 20

Ohms Law states that current is directionally proportional to current given that the conditions remain constant.

Question 21

Resistance in a series circuit…

Answer 21

the sum of each resistor equals the total resistance.

Question 22

Resistance in a parallel circuit…

Answer 22

the sum of the reciprocal resistances equals the total resistance.

Question 23

Drift Velocity Equation

Answer 23

Current = number of charged particles x cross sectional area x velocity x charge

Question 24

Power Definition

Answer 24

Rate of energy transfer over time

Question 25

Power Equation

Answer 25

Power = Voltage x Current

Question 26

How do you use power to find energy transfer?

Answer 26

Multiply power by time to find energy transfer.

Question 27

EMF Definition

Answer 27

Energy transferred to a unit charge

Question 28

EMF Equation

Answer 28

EMF = Energy Transfer / Charge

Question 29

What is EMF measured in?

Answer 29

Volts / V

Question 30

EMF Key Facts

Answer 30

Emf is the product of the total resistance within a circuit, it is the sum of P.D. in a closed circuit, EMF energy into circuit is equal to the P.D. out of the circuit.

Question 31

What is internal resistance?

Answer 31

Resistance within a battery which is caused by electrons colliding with atoms inside the battery so some energy is lost before electrons leave the battery.

Question 32

Internal Resistance Equation

Answer 32

EMF = Terminal P.D. + Lost Volts = Current (Load Resistance + Internal Resistance)

Question 33

What would happen if there is no internal resistance?

Answer 33

The terminal P.D would equal the EMF.

Question 34

What is terminal P.D.?

Answer 34

The voltage across the load resistor

Question 35

What does a graph for EMF and Internal Resistance look like?

Answer 35

y - axis = Voltage, x - axis = Current, y - intercept = EMF and gradient = - Internal Resistance

Question 36

What is a potential divider?

Answer 36

A circuit that has two or more resistors, that is series and when an output is placed across one of the resistors.

Question 37

What are potential dividers used for?

Answer 37

It is used to predictably vary the proportion of a supply the output receives.

Question 38

Potential Divider Equation

Answer 38

Voltage Out = Voltage In x Resistance 2 / Resistance 1 + Resistance 2

Question 39

What can the variable resistor be replaced by?

Answer 39

A thermistor or LDR

Question 40

Resistivity Definition

Answer 40

A measure of how easily a material conducts electricity.

Question 41

Resistivity Equation

Answer 41

Resistance x Cross-Sectional Area / Length

Question 42

What happens in an ohmic conductor?

Answer 42

In an ohmic conductor as you increase P.D. the energy transferred to each electron increases so they collide with greater force increasing drift velocity. This means that current increases as I = nAqv and V is directly proportional to I. AS resistance is inversely proportional resistance is 1/R.

Question 43

Example of an Ohmic Conductor

Answer 43

Wire or Resistor

Question 44

What happens in a semi-conductor?

Answer 44

As current increases so does the temperature this means that the number density increases as more free electrons are released so resistance decreases however it does not obey ohms law a temp increases so P.D. does not increases proportionally.

Question 45

Example of a Semi-Conductor

Answer 45

Thermistor and LDR

Question 46

What happens in a Filament Bulb?

Answer 46

In a filament bulb as P.D. increases the energy of electrons increases so there is greater energy in collisions with ions. This causes temperature to increase so metal ions vibrate with a greater amplitude further increasing collision rate. The resistance increases and as temperature increases it does not obey ohms law V = IR so current does not increase proportionally.

Question 47

What happens in a Diode?

Answer 47

The forward bias of a diode is the direction in which it will allow current to flow past the threshhold P.D. Above the threshold P.D. electrons move up an energy level to the conduction band so the number of free electrons increases and as I = nAqv current also increases.