Electric Circuits

Question 1

What is the purpose of an electric circuit

Answer 1

To transfer energy from the power source to the components where it is converted into useful forms

Question 2

Why must a circuit be complete

Answer 2

So that the charges are able to travel around the circuit and deliver energy

Question 3

Current definition

Answer 3

The rate of flow of charge

Question 4

What is the unit for for current and what apparatus do we use to measure current

Answer 4

Amps

Ammeter

Question 5

Which circuit is current the same at all points of the circuit and why

Answer 5

Series circuit because the charges can only flow along one path

Question 6

Why do parallel circuits have varying current

Answer 6

The charges can follow a choice of paths around the circuit
The current spots at a junction and rejoins at a junction do the current into a junction is the same as the current out of the junction

Question 7

What is conventional current

Answer 7

Electrons flow from the positive terminal to the negative terminal because they didn’t know about electrons

Question 8

Which way do electrons really flow through the circuit and why

Answer 8

Actually flow from the negative terminal to the positive terminal because the electrons which are negative repel against the negative terminal and are attracted to the positive terminal

Question 9

Equation for current

Answer 9

Current = charge/ time

Question 10

What equation links time, current and charge

Answer 10

Current = charge/ time

Time = charge / current

Charge = current x charge

Question 11

Series circuit (4)

Answer 11

Only have one path

If a component breaks in the circuit the whole circuit turns off

Energy has to be split between each component so light bulbs are dim

Current stays the same though out the circuit

Question 12

Parallel circuit (4)

Answer 12

Have lots of paths and branches

If a component breaks the circuit still works for the other components

All the energy from one electron can be given to each component, doesn’t need to share, so the bulb is brighter. Each branch receives the same amount of energy per coulomb

Current changes as electrons split off to different branches of the circuit

Question 13

Advantages to series circuits (3)

Answer 13

Easy to construct

Less wiring to connect more components to the circuit

Whole circuit can be controlled by a switch

Question 14

Disadvantages of series circuits (2)

Answer 14

Bulbs will be dimmer as energy is being shared

If one component breaks the whole circuit doesn’t work

Question 15

Advantages of parallel circuits (3)

Answer 15

All the bulbs are brighter as the energy is not being shared

If a component breaks the rest of the circuit still works

Each component can be individually controlled

Question 16

Disadvantages to parallel circuits (1)

Answer 16

Hard to construct if you want to add another component

Question 17

Voltage definition

Answer 17

A measure of how much energy is given to or taken away from a coulomb of charge as it passes around a circuit

Question 18

How is potential difference measured

Answer 18

Using a voltmeter

It is placed in parallel so that energy per coulomb before a component can be compared to after

Question 19

What other unit can potential difference be measured in

Answer 19

Joules per coulomb

This is because of the equation that links voltage, energy transferred and charge

Question 20

Equation for voltage

Answer 20

Voltage = energy transferred/ charge

Question 21

What equation links energy transferred, charge and potential difference

Answer 21

Potential difference = energy transferred/ charge

Energy transferred = potential difference x charge

Charge = energy transferred/ potential difference

Question 22

What is linked to current and voltage

Answer 22

resistance

Question 23

What is resistance

Answer 23

A measure of how difficult it is for a current to pass through a component. Resistance is measured in Ohms using an ohmmeter

Question 24

What is the the equation that links voltage, resistance and current

Answer 24

Voltage = resistance x current

Question 25

What is the relationship between current and voltage for a resistor What would the graph look like

Answer 25

As voltage increases, current increases so they have a directly proportional relationship So if voltage doubles then current doubles V🐟I Straight line with a positive correlation through the origin

Question 26

What happens to the current and voltage if a component has a higher resistance

Answer 26

There needs to be a higher voltage in order to have the same current pass through the component as it would be harder to get past it as it has a higher resistance

Question 27

Where does resistance come from

Answer 27

The electron carrying energy collide with the atoms in the component and lose some of their energy causing the atoms in the component to vibrate and heat up

Question 28

What is the relationship between voltage and current through a metal filament lamp What would it look like on the graph Why is this

Answer 28

Voltage and current are not directly proportional The line is a curved shape on the graph through the origin To get bigger currents, even larger voltages are needed as more energy is being transferred to heat energy in the lamp

Question 29

What is the relationship between voltage and current through a diode What does the graph look like

Answer 29

As voltage increases current also increases however there needs to be high enough voltages to get current as resistance is very very high Straight horizontal line so current is 0, then smooth curve upwards at higher voltages

Question 30

Why must voltages be high for current to pass through a diode And say something about which way current has to flow in a diode

Answer 30

Coulombs of charge need a certain amount of energy to pass through a diode as there is very high resistance The symbol tells us that current needs to flow the conventional way, this means that current can only flow one way through the diode

Question 31

Why do thermistors not behave like normal conductors

Answer 31

The resistance of a thermistor decreases as temperature increases as thermistors are made out of semiconductors