Topic 2.0: Controlling The Flow Of Electrical Current

Question 1

Conductors

Answer 1

Electrons are not tightly bound to the nuclei. They are freer to move.
Copper wire is a good electrical conductor. Other good conductors include: silver, Mercury and gold
Tap water is a conductor of electricity because of the many dissolved minerals it contains compared to the resistor of distilled water.
When no voltage is applied the electrons move around
When voltage is applied they all move in the same direction to the right

Question 2

Superconductors

Answer 2

Have no resistance to the flow of electrons

They electrical conductivity decreases as the resistance to electron flow increases.

Question 3

Insulators

Answer 3

Electrons are tightly bound to the nuclei.. They are not free to move.
Plastic or rubber are good insulators

Question 4

Resistors

Answer 4

A type of conductor
Allows electric current to pass but provides resistance to do it. This limits the amount of current.
Distilled water acts as a resistor. The more charged particles that a solution had the better it conducts. Distilled water is not a good conductor because it contains only water molecules which have no electrical charge

Question 5

Resistance

Answer 5

Is the measure of how difficult it is for electrons to flow through a substance
Measured in ohms.
The more resistance a substance has, the more the substance gains energy from each electron that passes through it
The energy gained by the substance is radiated to its surroundings as either heat or light energy.

Question 6

Variable resistors or rheostats

Answer 6

Can gradually increase or decrease the amount of current in a circuit
Used to dim lights

Question 7

Modelling voltage

Answer 7

Electricity can be compared to water:
Electricity comes from a source
Electricity encounters resistance
The more electrons the more powerful the current is in a conductor

Question 8

Electrical generators

Answer 8

Keeps electrons flowing from the negatively charged terminal to the positively charged one

Question 9

Modelling resistance and current

Answer 9

The amount of resistance in a circuit affects the electrical current
The current decreases as resistance is added
The shorter and thicker the wire, the less resistance it creates for electrons

Question 10

Ohms law

Answer 10

States that as long as temp stays the same:
The resistance of a conductor stays constant and the current is directly proportional to the voltage applied
If voltage in a current increases, the current also increases
If a resistor of greater value is used but voltage stays the same, the current decreases

Question 11

Voltage

Answer 11

Symbol: V
Unit: volts
Calculated by: current X resistance t
Measured with: voltmeter
Is potential difference between to points
A millivoltmeter is used to measure small voltages

Question 12

Current

Answer 12

Symbol: I
Unit: amperes (A)
Calculated by: voltage divided by resistance
Measured with: ammeter
Small currents are measured using a device called a galvanometers

Question 13

Resistance

Answer 13

Symbol: R
Unit: ohms
Calculated by: voltage divided by current
Measured with: ohmmeter 
Lowest when a conductor is cool
As temp increases resistance increases

Question 14

Relationships between voltage, current and resistance

Answer 14

Voltage/ current: directly related because current is the measure of voltage that goes through a circuit
Current/ resistance: when there is more resistance it affects the current( bigger pipes have less resistance than smaller pipes)

Question 15

Schematic or schematic design

Answer 15

Diagram using standardized symbols to show the components and connections in a circuit
Four basic parts:
A source- provides energy and electron supply
A conductor- provides path for current
A switching mechanism- controls current flow ( off & on)
A load- converts electricity to other forms of energy

Question 16

Schematic design symbol descriptions (11)

Answer 16

Conductor: conducts electricity through circuit
Cell: stores electricity ( large bar is positive)
Battery: combination of cells
Lamp: converts electricity to light
Resistor: controls the amount of current in the circuit
Ammeter: measures amount of current in circuit
Voltmeter: measures voltage across a
device in a circuit
Rheostat: variable resistor
Motor: converts electricity to mechanical energy
Fuse: melts if current is too high

Question 17

Difference between a cell and a battery in a schematic design

Answer 17

A battery is made up of many cells

Put together to create an energy source for the circuit

Question 18

Series circuit

Answer 18

Circuit in which the current passes through each bulb in turn. There is only one path for electricity!
When you add more bulbs the resistance increases, therefor the current decreases, causing the lights to dim

Question 19

Parallel circuit

Answer 19

Have a separate current path for each section of the circuit.
Your house is wired with parallel circuits so than you can shut off one light without shutting off ALL the power

Question 20

Transistors

Answer 20

Device usually with 3 layers arranged such that a small voltage in the middle layer controls a current between the outer layers
Allowing it to be used as a switch or amplifier

Question 21

When the power on resistance is negative or positive when calculating voltage…

Answer 21

Negative: move however many decimal places to the left
Positive: move however many decimals to the right

Question 22

Calculating power

Answer 22

Power (watts)
P= V x I 
Voltage times current= power
P= V x I
I= P divided by V
V= p divided by I

Question 23

Convert watts to kilowatts

Answer 23

Watts divided by 1000

Question 24

Multiply the hours given in problem

Answer 24

Kilowatts x hrs= Wh

Question 25

Kilowatt hours

Answer 25

Power x hours

P= V x I