Electricity

Question 1

Define current

Answer 1

Net flow of charged particles per unit time

Question 2

Define potential difference

Answer 2

• Energy transferred per unit charge when electrical energy is converted into another form of energy
• 1V = 1 J/C

Question 3

Define resistance

Answer 3

A materials opposition to the flow of electric current

Question 4

Define Ohm’s Law

Answer 4

For a given material, voltage is directly proportional to current at a constant temperature

Question 5

What are I-V characteristics?

Answer 5

Graph showing how current flowing through a component changes with increasing voltage

Question 6

Describe the I-V characteristics graph for an ohmic conductor

Answer 6

Straight constant gradient

Question 7

Describe the I-V characteristics graph for a filament lamp

Answer 7

• Bottom left is increasing curved gradient
• Top right has decreasing curved gradient

Question 8

Describe the I-V characteristics graph for a diode

Answer 8

• Far end of negative p.d has very low negative current
• Current doesn’t go above 0 until V > 0.6
• After 0.6V, gradient curves upward steeply

Question 9

Define resistivity

Answer 9

A property of a material that determines the resistance of a piece of given dimensions

Question 10

What is units for resistivity?

Answer 10

Ωm / ohm metres

Question 11

What are semiconductors?

Answer 11

• A group of materials which conduct electricity, but not as good as metals
• When temperature rises, they can release more carriers and their resistance decreases

Question 12

State 3 common semiconductor components

Answer 12

• Thermistors
• Diodes
• Light dependent resistors(LDR)

Question 13

What is a thermistor?

Answer 13

• A component with a resistance that changes with temperature
• Resistance decreases as temperature increases
• Temperature is normally controlled using a water bath

Question 14

What is a LDR?

Answer 14

• A component with a resistance that changes with light intensity
• Resistance decreases as light intensity increases

Question 15

What is a superconductor?

Answer 15

A material that has zero resistivity and zero resistance when cooled below a critical temperature

Question 16

State 3 uses of superconductors

Answer 16

• Power cables that transmit electricity without power loss
• Really strong electromagnets with applications such as Maglev trains
• Electronic circuits that work really fast with minimal energy loss due to having no resistance to slow current down

Question 17

Define power

Answer 17

Energy transferred per second in Watts

Question 18

What is the equation for Energy involving power?

Answer 18

E = Pt

Question 19

Define internal resistance

Answer 19

The resistance of the materials within the battery

Question 20

How does internal resistance occur?

Answer 20

Electrons in the chemical reactions collide with the atoms in the battery, losing energy which causes resistance

Question 21

Define electromotive force, emf

Answer 21

• Energy transferred from chemical to electrical energy in a power system
• Electrical energy per unit charge, in volts

Question 22

Define terminal p.d

Answer 22

• Energy transferred from electrical energy to another type
• Work done per unit charge, in volts

Question 23

For a V-I graph, what does the y-intercept represent?

Answer 23

emf

Question 24

For a V-I graph, what does the gradient represent?

Answer 24

Negative internal resistance

Question 25

State Kirchoff's first law and the principle it's based on

Answer 25

- Sum of the currents entering a circuit = Sum of the currents leaving the circuit - Conservation of charge

Question 26

State Kirchoff's second law and the principle it's based on

Answer 26

- Sum of the EMFs around a circuit loop = Sum of the PDs around that loop - Conservation of energy

Question 27

What is constant in a series circuit?

Answer 27

Current

Question 28

What is constant in a parallel circuit?

Answer 28

Voltage

Question 29

How do you find the total emf of cells in a series circuit?

Answer 29

ϵ(total) = ϵ1 + ϵ2 + ϵ3

Question 30

How do you find the total emf of cells in a parallel circuit?

Answer 30

- ϵ(total) = ϵ1 = ϵ2 - When cells are identical

Question 31

What is a potential divider?

Answer 31

- A circuit containing a voltage source and a pair of resistors - The voltage across one resistor is used as an output voltage - If resistors aren't fixed, the circuit will be capable of producing a variable output voltage

Question 32

State the relationship between resistance and length

Answer 32

Resistance is proportional to length

Question 33

State the relationship between resistance and cross-sectional area

Answer 33

Resistance is inversely proportional to cross-sectional area

Question 34

State the relationship between temperature and resistance for a metal conductor

Answer 34

As temperature increases, resistance increases

Question 35

Describe the relationship between temperature and resistance for a metal conductor

Answer 35

- Resistance increases as temperature increases - As fixed ions of the metal gain energy and vibrate - This causes charge carriers to collide more, making them slow down - Therefore current decreases, which increases resistance

Question 36

State the equation for the output voltage of a potential divider?

Answer 36

V(out) = R(2) x V(in)/ R(1) + R(2)