Electricity

Question 1

I know that there are two types of electrical charge

Answer 1

Positive
Negative

Like charges repel and unlike charges attract. The direction of the force on the charge will depend on the sign of the charge

Question 2

I know the defination of electrical current

Answer 2

Electrical current is defined as the charge transferred (flowing) in a circuit per second

Question 3

I can use the formula that relates charge, current and time

Answer 3

Q = I x t

Q = charge
I = current
t = time

Question 4

I know the difference between direct current and alternating current

Answer 4

Alternating current (a.c.) is when current in a circuit continually changes direction. a.c. is supplied from the mains

Direct current _d.c.) is when the current flows in one direction only around a circuit. Batteries supply d.c. current

Question 5

I know the effect of an electric field on a charge

Answer 5

Electric fields exist in the regions around electric charges. They can be reoresented by drawing field lines. The field is strongest when the field lines are closest together

Charged particles experience a force in an electrical field

On applying an electric field to a conductor for example, the free electric charges (electrons) experience a force and move

Question 6

I know that the potential difference (voltage) of a supply is a measure of the energy given to the charge carriers in a circuit

Answer 6

A 12V battery gives 12J of energy to each coulomb of charge in a circuit

A 230V supply gives 230J of energy ti each coulomb of charge in a circuit

Question 7

Cell

Answer 7

Sourceof electrical energy

Question 8

Battery

Answer 8

Two or more cells joined together

Question 9

Lamp

Answer 9

Changes electrical energy into light

Question 10

Switch

Answer 10

Used to make a complete circuit

Question 11

Resistor

Answer 11

Affects the current flowing in a circuit

Question 12

Variable Resistor

Answer 12

Allows the current in a circuit to be changed

Question 13

LED (light-emiting diode)

Answer 13

Changes electrical energy into light

uses less current than a lamp

Question 14

Motor

Answer 14

Changes electrical energy into kenetic energy

Question 15

Loudspeaker

Answer 15

Changes electrical energy into sound energy

Question 16

Photovoltaic cell

Answer 16

Changes light energy into electrical

also known as a solar cell

Question 17

Fuse

Answer 17

Desgined to protect an appliance by melting if the current is too high

Question 18

Diode

Answer 18

Allows current to flow in one direction only

Question 19

Capacitor

Answer 19

Stores charge

Question 20

Thermistor

Answer 20

The resistance of a thermistor depends on temperature

Question 21

LDR (light dependent resistor)

Answer 21

The resistance of an LDR depends on light intensity

Question 22

NPN transistor

Answer 22

Acts as an electronic switch

Question 23

MOSFET transistor

Answer 23

Acts as an electronic switch

Question 24

I know an LED lights only when connected into a circuit the correct way around

Answer 24

An LED is made up of two special materials called semiconductors joined together
For an LED to light the positive terminal of the LED must be connected to the positive terminal of the power supply
LEDs come in colours of red, green, yellow, blue and white
For a correctly connected LED to light up the voltage accross the LED must be above the “switching on” voltage for that LED
As soon as this voltage is reached the LED switches on, thereafter increasing the voltage across the LED will increase the brightness of the LED

Question 25

I know why an LED always has a resistor connected in series with it

Answer 25

An LED will brake if too high a current passes through it or if there is too high a voltage across it. To prevent this an LED must always be connected in series with a protective resistor

Question 26

I know the current and voltage relationships in a series circuit

Answer 26

In a series circuit the battery/power supply and circuit components are connected in a continuous loop There is only one path for current in a series circuit and so the current is the same at all points Isupply = I1 = I2 = I3 = ... The sum of all the voltages across components in series is equal to the supply voltage Vsupply = V1 + V2 + V3 + ...

Question 27

I know the current and voltage relationships in a parallel circuit

Answer 27

In a parallel circuit there are many paths around the circuit The current in the individual paths add up to the current in the main circuit Isupply = I1 +I2 + I3 + ... The voltages across the comonents in the circuit are the same Vsupply = V1 = V2 = V3 = ...

Question 28

I can use the appropriat eformula to calculate resistance in a series circuit

Answer 28

RT = R1 + R2 + R3 + ... RT = Total Resistance of the circuit (measured in ohms) R1 = Resistance of component 1 (measured in ohms) R2 = Resistance of component 2 (measured in ohms) R3 = Resistance of component 3 (measured in ohms) When resistors are combined in series the total resistance increaces

Question 29

I can use the appropriate formula to calculate resistance in a parallel circuit

Answer 29

1/RT = 1/R1 + 1/R2 + 1/R3 + ... R1 = Resistance of component 1 (measured in ohms) R2 = Resistance of component 2 (measured in ohms) R3 = Resistance of component 3 When resistors are combined in para;;e; tje tpta; resostamce decreases

Question 30

I can use a V - I graph to determine resistance

Answer 30

Using the following circuit a sample set of results can be generated to plot a V - I graph - The graph shows that as the voltage across the component increases, the current through the component also increases - The graph also shows the link between Voltage and Current - The cradient of the graph can be found for any point by dividing V/I - For the graph above the gradient is constated - This constant is called the resistance of the component

Question 31

i can use the formula that relates voltage, current and resistance

Answer 31

V = I x R ``` V = Voltage (measured in volts, V) R = Current (measured in amperes, A) R = Resistance (measured in ohms) ```

Question 32

I know that a transistor can be used as a switch

Answer 32

Transistors can be thought of as electronic switches which have no moving parts The following are two examples of a transistor: - n-channel MOSFET - npn - transistor When the voltage across a trajsistor reaches a certain value called the switching on voltage the transistor switches on. When the voltage across the trainsistor drops below this value the transistor switches off Different types of transistor have different switching on voltages

Question 33

I know the relationship between temperature and resistance of a conductor

Answer 33

As the temperature of a conductor increases its resistance increases When a conductor is heated, the atoms vibrate with grater amplitude. This makes it more difficult for electrons to move through the material