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