Electricity

Question 1

Define electric current

Answer 1

The rate of flow of electric charge

Question 2

What is the unit of current?

Answer 2

Amperes

Question 3

What is 1 amp equal to?

Answer 3

A charge of 1 coulomb flowing in 1 second

Question 4

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

Answer 4

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

Question 5

What is an electrolyte?

Answer 5

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

Question 6

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

Answer 6

The charge transferred

Question 7

Define potential difference

Answer 7

Energy transferred per unit charge between two points

Question 8

Do voltmeters go in series or parallel?

Answer 8

parallel

Question 9

Define the electromotive force

Answer 9

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

Question 10

What are lost volts?

Answer 10

The p.d across the “Internal resistor”.

Question 11

What are lost volts equal to?

Answer 11

The energy wasted by the cell per coulomb of charge

Question 12

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

Answer 12

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

Question 13

Define resistance

Answer 13

the opposition of the conductor to the electric current flowing through it

Question 14

What is a superconductor?

Answer 14

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

Question 15

Name an applications of superconductors

Answer 15

Power cables which reduce energy loss

Question 16

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

Answer 16

Straight line through the origin

Question 17

State Ohms law

Answer 17

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

Question 18

Describe the IV graph for a filament lamp

Answer 18

increasing gradient then decreasing gradient

Question 19

Describe the IV graph for a diode

Answer 19

Flat until the origin then it has an increasing gradient

Question 20

What is a thermistor?

Answer 20

A component whose resistance varies with temperature

Question 21

Do thermistors have a positive or negative temperature coefficient?

Answer 21

negative

Question 22

What happens when the temperature increases in a thermistor?

Answer 22

It’s resistance decreases

Question 23

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

Answer 23

It increases

Question 24

How can thermistors be used?

Answer 24

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

Question 25

What is resistivity?

Answer 25

A measure of how easily a material conducts electricity

Question 26

What does the resistivity of a substance depend on?

Answer 26

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

Question 27

Is resistivity dependant on environmental factors?

Answer 27

Yes

Question 28

Define power

Answer 28

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

Question 29

State Kirchhoff's first law

Answer 29

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

Question 30

State Kirchhoff's second law

Answer 30

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

Question 31

What does internal resistance do?

Answer 31

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

Question 32

How is internal resistance caused?

Answer 32

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

Question 33

Do Ammeters go in series or parallel?

Answer 33

series

Question 34

What is the resistance of an ideal ammeter?

Answer 34

zero

Question 35

What is the resistance of an ideal voltmeter?

Answer 35

Infinity

Question 36

What components make up a potential divider circuit?

Answer 36

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

Question 37

How is a potential divider circuit set up?

Answer 37

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

Question 38

What is a use of potential divider circuits?

Answer 38

Sensor circuits

Question 39

How do LDR's work?

Answer 39

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

Question 40

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

Answer 40

Because it is a straight line through the origin

Question 41

What are 2 rules of series circuit?

Answer 41

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 42

What are 2 rules of series circuit?

Answer 42

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

Question 43

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

Answer 43

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