3.5.1 Current Electricity

Question 1

What is current?

Answer 1

Current is the rate of flow of electric charge (electrons) around a circuit
I

Question 2

What is current measured in?

Answer 2

Amps (A)/Milliamps(mA)

Question 3

What is potential difference?

Answer 3

The difference in potential between two charged plates driving electrons around a circuit to reach the positive plate (The work done per unit charge)
V

Question 4

What is potential difference measured in?

Answer 4

Volts (V)

Question 5

What is resistance?

Answer 5

A quantity describing how ‘difficult’ the electrons find it to be able to move through a wire/component
R

Question 6

What is resistance measured in?

Answer 6

Ohms(Ω)

Question 7

What is charge?

Answer 7

Each electron has a negative charge so the more current there is, the more charge
Q

Question 8

What is charge measured in?

Answer 8

Coulombs (C)

Question 9

What is the negative charge of an electron?

Answer 9

1.6*10-19 coulombs

Question 10

What is power?

Answer 10

The rate at which electrical energy is supplied to a circuit

P

Question 11

What is power measured in?

Answer 11

Watts (W) / Joules per second (J/s)

Question 12

Q=It

Answer 12

Charge = Current * time
C A s
Q I t

Question 13

V=IR

Answer 13

Potentical difference = Current * Resistance
V A Ω
V I R

Question 14

V=W/Q

Answer 14

Potential difference=Work done/Charge
V J C
V W Q

Question 15

P=IV

Answer 15

Power = Current*Potential difference
W(J/s) A V
P I V

Question 16

P=(V*V)/R

Answer 16

Power= (Potential difference*Potential difference)/ Resistance
W(J/s) V Ω
P V R

Question 17

P=IIR

Answer 17

Power=CurrentCurrentResistance
W(J/s) A Ω
P I R

Question 18

What is a watt(W) equal to?

Answer 18

Watt(W) = Joule/second (J/s)

Question 19

What is electrical energy?

Answer 19

watt(W)*second(s)=electrical energy

Question 20

In ohmic conductors, what is the relationship between potential difference and current?

Answer 20

Current is directly proportional to potential difference

I∝V

Question 21

What does this mean on a graph I∝V?

Answer 21

Current is directly proportional to potential difference therefore the results should be a straight line where the gradient is the resistance

Question 22

What is an ohmic conductor?

Answer 22

A conductor which obeys the law of ohm

Question 23

In ohmic conductor graphs, what does a steep line mean?

Answer 23

In ohmic conductor graphs, the steeper the line, the lower the resistance

Question 24

What occurs in non-ohmic conductors?

Answer 24

• As potential difference increases
• Temperature increases
• Causing the resistance to increase
• Limiting the current
• Same occurs in the negative bias

Question 25

What are filament bulbs an exanple of?

Answer 25

Filament bulbs are an example of non-ohmic conductors

Question 26

How do filament bulbs work?

Answer 26

- Consists of a thin metal wire - Temperature does not remain constant - The metal wire heats up - Causing light to be produced

Question 27

How does the increasing of voltage limit the current in filament bulbs?

Answer 27

- Potential difference increases, increasing temperature - Higher the temperature, the more the particles vibrate - The vibraring particles increases the difficulty of the electrons to pass through - This increase in resistance impedes the movement of the electrons - This limits the current - flow of electric charge

Question 28

Does the actions which occur in non-ohmic conductors also occur in the negative bias?

Answer 28

The current is also limited in the negative bias in non-ohmic conductors

Question 29

What is a forward bias in a diode?

Answer 29

The forward bias is where a diode only conducts when the current is in the direction of the arrowhead on the circuit symbol

Question 30

When does a diode conduct?

Answer 30

A diode only conducts when the current travels in the direction of the arrowhead on the circuit symbol, known as the forward bias

Question 31

What is a diode used for?

Answer 31

A diode is used to change an AC supply into a DC supply

Question 32

Why is a resistor used before a diode?

Answer 32

The resistor limits the amount of current so no overheating occurs

Question 33

Why can diodes break easily?

Answer 33

- Tiny change in potential difference - Cause huge change in current - Huge current causes huge resistance - Increases temperature, busting the circuit

Question 34

What can be used to prevent a diode from busting?

Answer 34

A resistor to limit the current

Question 35

What is the best amount of potential difference used in a diode called?

Answer 35

The threshold potential differencde (0.6V)

Question 36

What is Ohm's Law?

Answer 36

Ohm's law is the potential difference across a metallic conductor is proportional to the current through providing the physical conditions do not change

Question 37

Why do ammeters have hypothetically 0 resistance?

Answer 37

Used to measure current though a resistor therefore must be in series so same current passes through therefore it can have no resistance

Question 38

Why do voltmeters have hypothetically infinite resistance?

Answer 38

Used to measure potential difference across a resistor therefore must b parallel so no current should pass through otherwise the ammeter would record the wrong current

Question 39

Where are semiconductors used in?

Answer 39

Sensors

Question 40

Why don't semiconductors conduct as well as metals?

Answer 40

Fewer charge carriers available

Question 41

Why are semiconductors excellent at detecting changes in their environment?

Answer 41

When more energy is supplied, more charge carriers can be released therefore increasing current

Question 42

What are examples of semiconductors?

Answer 42

- Thermistors | - Diodes