2.4 - Energy Transfers Flashcards Preview

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Flashcards in 2.4 - Energy Transfers Deck (15):
1

In an electrical circuit, what is power?

The rate at which electrical energy is transfered.

2

What is the unit of power?

Watt (W)

3

What symbol is normally used to represent power in equations?

P

4

How could you calculate power from potential difference and current?

Power = current x potential difference

[P = I V]

5

If you do not know the potential difference in a circuit, how can you calculate power?

Use P = I V and V = I R together:

P = I (I R)

P = I² R

6

How do electrical appliances normally work?

They transfer electrical energy into another form of energy (e.g. heat and kinetic for a hairdryer)

7

What factors affect how much energy an appliance uses?

  • The power of the appliance (more powerful appliances use more power each second they are on)
  • The length of time the appliance is turned on for

8

In an electrical circuit, when is work done?

Work is done when charge flows in a circuit

9

What is the unit for energy?

Joules (J)

10

What symbol is normally used to represent energy in an equation?

E

11

How would you calculate how much energy is transfered by an appliance?

Energy Transferred = Power × time [E = P t]

Or, we can use P = I V and I = Q / t:

  • E = P t
  • E = I V t
  • E = (Q / t) V t
  • E = Q V

12

What is the National Grid?

A system of:

  • cables
  • transformers which allow electrical power to be transferred from power stations to consumers.

13

What is a step-up transformer?

A component which increases the potential difference along a cable. Current (I) is decreased, so power transferred remains the same (P = I V)

14

What is a step-down transformer?

A component which decreases the potential difference along a cable. Current (I) is increased, so power transferred remains the same (P = I V)

15

Why are transformers used in the National Grid?

  • Energy is wasted as heat when current flows through a wire.
  • The higher the current, the more heat is lost
  • To reduce this loss, the National Grid transmits electricity at a low current
  • It uses a step-up transformer to increase the voltage along the wire (and decrease current)
  • It uses a step-down transformer to decrease the voltage back to a safe level for use in homes