B.5 Currents and Circuits

Question 1

Current (I)

Answer 1

Rate of flow of electric charge (Cs-1 / A)

Question 2

Charge carriers in electrical circuits

Answer 2

Electrons

Question 3

Elementary charge (e)

Answer 3

Charge of a single electron (1.6 x 10^-19)

Question 4

Conductor

Answer 4

A material that allows flow of charge through it due to carriers (electrons)

Question 5

When do charge carriers (electrons) move within conductors?

Answer 5

When an electrical field is created within the conductor

Question 6

Potential difference (V)

Answer 6

The work done or energy transferred per unit of charge on moving a positive charge between two points along the path of a current

Question 7

Series circuit - current

Answer 7

Same around the circuit

Question 8

Series circuit - potential differences

Answer 8

Sum of the potential differences across components add to the potential difference across the power supply

Question 9

Parallel circuit - current

Answer 9

Splits across branches

Question 10

Parallel circuit - potential difference

Answer 10

Is the same across every branch

Question 11

Ammeter

Answer 11

Device used to measure current. Must be connected in series.

Question 12

Voltmeter

Answer 12

Used to measure potential difference. Must be connected in parallel.

Question 13

Resistance (R)

Answer 13

The ratio of potential difference across a component to the current flowing through the component (ohms)

Question 14

Resistor def

Answer 14

A component whose resistance is constant over a range of potential differences

Question 15

Ohms’s Law

Answer 15

The current flowing through a piece of metal is proportional to the potential difference across it providing the temperature remains constant

Question 16

Ohmic

Answer 16

A metal conductor at a constant temperature and constant resistance

Question 17

Non-ohmic

Answer 17

A metal conductor whose resistance changes due to a temperature increase

Question 18

Ideal ammeter

Answer 18

Resistance of 0 so it does not affect the current

Question 19

Ideal voltmeter

Answer 19

Infinite resistance so it does not draw any current

Question 20

What do resistors do?

Answer 20

They have a heating effect - the electrical potential energy of charge carriers is converted into heat energy

Question 21

How do resistors heat?

Answer 21

Electrons flowing through the circuit collide with positive ions in the metal of the resistor and lose energy to them. Ions gain Ek and metal heats up due to increase in Ek

Question 22

Variable resistor

Answer 22

A resistor whose resistance can be changed

Question 23

Resistivity (p)

Answer 23

Property of a substance that gives a measure of how the substance opposes the flow of electric current

Question 24

Potentiometer

Answer 24

A single resistor that can be used to divide up the potential difference

Question 25

Light dependent resistor

Answer 25

Resistor whose resistance is dependent on the intensity of the light that falls upon it

Question 26

As light intensity increases…

Answer 26

Resistance decrease on a LDR

Question 27

As light intensity decreases…

Answer 27

Resistance increases on a LDR

Question 28

Thermistor

Answer 28

A resistor whose resistance is dependent on its temperature

Question 29

As temperature increases,

Answer 29

The resistance of the thermistor decreases

Question 30

As temperature decreases

Answer 30

the resistance of the thermistor increases

Question 31

Electrical power

Answer 31

Amount of energy used or supplied per unit time

Question 32

Chemical cell

Answer 32

Cell used to produce a direct current. Inside of the cell, chemical reactions occur and chemical potential energy is converted to electrical potential energy.

Question 33

How does a chemical cell work?

Answer 33

Free electrons in the circuit are repelled by the negative terminal and are attracted to the positive terminal. Move around the circuit. While current flows, chemicals in the cell react and give energy to the electrons as they pass through.

Question 34

Primary cell

Answer 34

Cannot be recharged, irreversible chemical reaction, once chemicals have been used, it no longer produces electrical energy.
Examples include Zn-C and alkaline batteries

Question 35

Secondary cells

Answer 35

Designed to be recharged, reversible reaction, reversing the current through the cell by attaching it to an external DC power source will reverse the chemical reaction, producing more reactants. (Pb-Acid, Ni-Cd and Lithium Ion batteries)

Question 36

Solar cell

Answer 36

Convert solar to electrical energy. Produce a direct current. EMF of 1V. Often connected in series to create a higher emf. Efficiency of 25%

Question 37

Why would secondary cells be connected to solar cells?

Answer 37

As solar cells only produce electrical energy when exposed to sunlight so secondary cells will be charged to provide energy at night/cloudy days

Question 38

Internal resistance (r)

Answer 38

The materials the cell is made of has resistance.

Question 39

EMF

Answer 39

Energy supplied per unit charge by the cell to the circuit

Question 40

Terminal potential difference (V)

Answer 40

Measure of energy available to the external circuit

Question 41

What creates the electric field within a circuit?

Answer 41

Electric cells and power supplies