Electricity

Question 1

Define electric current

Answer 1

The rate of flow of electric charge

Question 2

Why does the resistance of an intrinsic semiconductor used in a thermistor decrease with increasing temperature?

Answer 2

The number of charge carriers increases

Question 3

What is the unit of current?

Answer 3

Amperes

Question 4

What is 1 amp equal to?

Answer 4

A charge of 1 coulomb flowing in 1 second

Question 5

What is the definition of an electronvolt?

Answer 5

The energy transferred to or from an electron when it is accelerated by a potential difference of 1V.

Question 6

What electric currents don’t involve the flow of electrons?

Answer 6

Charged ions in a solution (electrolyte) also flow and create a current

Question 7

What is an electrolyte?

Answer 7

A conducting solution usually containing positive and negative salt ions dissolved in water

Question 8

What does the area under a current-time graph represent?

Answer 8

The charge transferred

Question 9

Define potential difference

Answer 9

Energy transferred per unit charge between two points

Question 10

Do voltmeters go in series or parallel?

Answer 10

parallel

Question 11

Define the electromotive force

Answer 11

the amount of electrical work done (energy transferred) per unit charge that passes through the cell

Question 12

What are lost volts?

Answer 12

The p.d across the “Internal resistor”.

Question 13

What is stopping potential?

Answer 13

The potential difference required to stop electrons crossing a photoelectric cell

Question 14

What are lost volts equal to?

Answer 14

The energy wasted by the cell per coulomb of charge

Question 15

What is the law of conservation of energy in terms of voltage?

Answer 15

The sum of emf’s in a circuit equals the sum of p.ds

Question 16

Define resistance

Answer 16

the opposition of the conductor to the electric current flowing through it.
or the potential resistance required across a component of force a current of 1A to flow

Question 17

What is a superconductor?

Answer 17

A wire or device that has zero resistivity at and below a critical temperature

Question 18

Name an applications of superconductors

Answer 18

Power cables which reduce energy loss

Question 19

What does the IV graph of a fixed resistor look like?

Answer 19

Straight line through the origin

Question 20

State Ohms law

Answer 20

The current flowing through a wire is directly proportional to the potential difference across it as long as physical conditions are kept constant

Question 21

Describe the IV graph for a filament lamp

Answer 21

increasing gradient then decreasing gradient

Question 22

Describe the IV graph for a diode

Answer 22

Flat until the origin then it has an increasing gradient

Question 23

What is a thermistor?

Answer 23

A component whose resistance varies with temperature

Question 24

Do thermistors have a positive or negative temperature coefficient?

Answer 24

negative

Question 25

What happens when the temperature increases in a thermistor?

Answer 25

It's resistance decreases

Question 26

What happens to the resistance of a metal conductor when its temperature increases?

Answer 26

It increases

Question 27

How can thermistors be used?

Answer 27

They can trigger an event when the temperature reaches a specific value. e.g. heating systems

Question 28

On an IV graph for a thermistor what would happen if the temperature increased?

Answer 28

Gradient would increase

Question 29

What is resistivity?

Answer 29

A measure of how easily a material conducts electricity

Question 30

What does the resistivity of a substance depend on?

Answer 30

The resistance, cross sectional area of wire and length of wire

Question 31

Is resistivity dependant on environmental factors?

Answer 31

Yes

Question 32

Define power

Answer 32

The rate of energy transfer (Or the rate of doing work)

Question 33

State Kirchhoff's first law

Answer 33

At a circuit junction, the sum of currents flowing into the junction equals the sum of the currents flowing out of the junction

Question 34

State Kirchhoff's second law

Answer 34

In a closed circuit loop, the sum of potential drops is equal to the sum of the electromotive forces

Question 35

What does internal resistance do?

Answer 35

It creates a potential difference that leads to electrical energy being transferred to thermal energy inside the power supply

Question 36

How is internal resistance caused?

Answer 36

It is caused by electrons colliding with atoms inside the battery therefore some energy is lost before electrons even leave the battery

Question 37

How can you find internal resistance from a graph of p.d against current when varying a variable resistor.

Answer 37

The gradient (p.d/current)

Question 38

Do Ammeters go in series or parallel?

Answer 38

series

Question 39

What is the resistance of an ideal ammeter?

Answer 39

zero

Question 40

What is the resistance of an ideal voltmeter?

Answer 40

Infinity

Question 41

What components make up a potential divider circuit?

Answer 41

A power supply, a fixed resistor, a third resistive component

Question 42

what is a resistor?

Answer 42

A component designed to have a particular resistance, regardless of the current through it.

Question 43

How is a potential divider circuit set up?

Answer 43

All components in series and the emf is shared across the two resistive components

Question 44

What is a use of potential divider circuits?

Answer 44

Sensor circuits

Question 45

How do LDR's work?

Answer 45

With low light intensity, they have very high resistance and with high light intensity, they have very low resistance

Question 46

How can a graph show that the component follows Ohms law?

Answer 46

Because it is a straight line through the origin

Question 47

What are 2 rules of series circuit?

Answer 47

The current is the same everywhere in the circuit The total sum of the voltages across all elements is equal to the supply p.d

Question 48

What are 2 rules of series circuit?

Answer 48

The sum of the currents in each branch is equal to the total current The p.d across each branch is the same

Question 49

What happens when identical cells are joined in parallel? Why?

Answer 49

The total voltage is equal to the voltage of one cell. because the current is split equally between branches therefore the overall p.d is the same