2.4 - Energy Transfers Flashcards Preview

GCSE Physics - Delete Me > 2.4 - Energy Transfers > Flashcards

Flashcards in 2.4 - Energy Transfers Deck (15):

In an electrical circuit, what is power?

The rate at which electrical energy is transfered.


What is the unit of power?

Watt (W)


What symbol is normally used to represent power in equations?



How could you calculate power from potential difference and current?

Power = current x potential difference

[P = I V]


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


How do electrical appliances normally work?

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


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


In an electrical circuit, when is work done?

Work is done when charge flows in a circuit


What is the unit for energy?

Joules (J)


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



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


What is the National Grid?

A system of:

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


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)


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)


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