Electricity (2)- Pt 1

Question 1

Define current

Answer 1

• the flow of electric charge

- A (amps)

Question 2

Define potential difference (voltage)

Answer 2

• the driving force that pushes the charge round

- V (volt)

Question 3

Define resistance

Answer 3

Anything that slows down the flow of the current

-ohm (weird symbol)

Question 4

The current flowing through a component depends on the ……………….. across it and the ………………. of the component

Answer 4

Potential difference

Resistance

Question 5

What’s the formula that uses current, time and charge?

Answer 5

charge (C)= current (A) x time (s)

Q = It

Question 6

What’s the formula that links resistance, potential difference and current?

Answer 6

Potential difference (V) = Current (A) x Resistance (ohms)

Question 7

What happens to the resistance in a ohmic conductor?

Answer 7

• at constant temperature the current flowing through the ohmic conductor is directly proportional to the potential difference
• an ohmic conductor = a wire or a resistor

Question 8

The …………. must always be placed in series and the ………… is always placed in parallel

Answer 8

Ammeter

Voltmeter

Question 9

Explain why filament lamps aren’t ohmic conductors?

Answer 9

• because energy is transferred to the thermal energy store in the filament which is designed to heat up
• resistance increases with the temperature
• so as the current increases the filament heats up and the resistance increases

Question 10

Explain why diodes aren’t ohmic conductors?

Answer 10

• for diodes the resistance depends on the direction of the current
• they only let the current flow in 1 direction but have a high resistance in the oppposite direction

Question 11

How does an ohmic conductor look on a I-V graph?

Answer 11

-a straight line through the origin (its linear)

Question 12

What are the properties of a LDR?

Answer 12

• light dependent resistors
• it’s a resistor that depends on the intensity of light
• in bright light the resistance decreases
• in darkness the resistance increases
• used for: automatic nights lights and burglar detectors

Question 13

What are the properties of a thermistor?

Answer 13

• it’s a temperature dependant resistor
• when it’s hot, the resistance decreases
• when it’s cool, the resistance increases
• used for: temperature detectors (electronic thermostats)

Question 14

What’s a sensing circuit?

Answer 14

-it can be used to turn on or increase the power to components depending on the conditions that they’re in

Question 15

What are the components of a series circuit?

Answer 15

• potential difference is shared : V total = V 1 + V 2
• current is the same
• resistance is shared: R total = R 1 + R 2

Question 16

What are the components of a parallel circuit?

Answer 16

• potential difference is the same
• current is shared between branches
• adding a resistor in parallel reduces the total resistance

Question 17

Describe the properties of the UK mains supply

Answer 17

• it’s an alternating current
• approx 230V
• 50Hz

Question 18

What’s an alternating current?

Answer 18

They’re produced alternating voltages in where the positive and negative end keep alternating

Question 19

What kind if current supplies cells and batteries?

Answer 19

A direct current (always flowing in the sane direction)

Question 20

What are the names and colours of the 3 wires inside a cable?

Answer 20

Neutral wire- blue
Live wire-brown
Earth wire- green and yellow

Question 21

What does the live wire do?

Answer 21

(Brown)

-provides the alternating potential difference (230v) from the mains supply

Question 22

What does the neutral wire do?

Answer 22

(Blue)

• it completes the circuit and carries away the current
• electricity flows in through the live wire and out through the neutral wire. It’s around (0v)

Question 23

What does the earth wire do?

Answer 23

(Green and yellow)

• it’s for protecting the wiring and safety (it stops the appliance from becoming live)
• doesn’t usually carry a current only when something’s gone wrong it’s (0v)

Question 24

Explain how a live wire can give you an electric shock?

Answer 24

• your 0v, there’s a big pd between your body and the live wire with produces a current to flow through you
• even the plug socket is off and there’s no current flowing there’s still pd in the live wire
• connections between live and the earth can be dangerous. It provides a low resistance path to earth causing a huge current (which could lead to a fire)

Question 25

Define power

Answer 25

The power of an appliance is the energy that it transfers per second

Question 26

What’s the equation to find energy transferred?

Answer 26

Energy transferred (J) = power (W) x Time (s)
E = Pt

Question 27

What are power ratings?

Answer 27

-they’re labelled with the maximum (safe) operating power

Question 28

How do you find the energy transferred in a circuit?

Answer 28

Energy transferred (J) = charge flow (C) x potential difference (V)
E = Q.V.

Question 29

What are the 2 formula’s to find power?

Answer 29

Power (W) = pd (V) x Current (A)
P=VI
Power (W) = current2 (A) x resistance (ohms)
P = I2 R

Question 30

What is the is the national grid?

Answer 30

-a huge system of cables and transformers which connects power stations to consumers