6.1.1.4 PowerPower is defined as the rate at which energy is transferred or the rate at which work is done.power = energy transferred x time P = Etpower = work done x time P = Wt

• power, P, in watts, W• energy transferred, E, in joules, J• time, t, in seconds, s• work done, W, in joules, J

An energy transfer of 1 joule per second is equal to a power of 1 watt.Students should be able to give examples that illustrate the definition of power eg comparing two electric motors that both lift the same weight through the same height but one does it faster than the other.

STARTER: Match the letter with correct measurement, and name of units and the unit’s symbol.

Power

time

Work done

Energy transferred

Joules

Joules

seconds

Watts

W

t

P

E

J

W

s

J

STARTER: Match the letter with correct measurement, and name of units and the unit’s symbol.

Power

time

Work done

Energy transferred

Joules

Joules

seconds

Watts

W

t

P

E

J

W

s

J

STARTER: Match the letter with correct measurement, and name of units and the unit’s symbol.

Power

time

Work done

Energy transferred

Joules

Joules

seconds

Watts

W

t

P

E

J

W

s

J

Power - Aims

• Know that energy can be transferred to systems.

• Understand what power is energy transfer of 1 joule per second is equal to a power of 1 watt.

• Give examples that illustrate the definition of power

What is power?

• The power of a system depends on how many joules of energy is transferred every second.

• We measure power in Watts (W)• An energy transfer of 1 joule per second is equal

to a power of 1 watt. So 1 watt = 1 joule per second

So, the more joules of energy transferred per seconds, the greater the power of the system.

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Comparing the power of two motorsCompare two electric motors that both lift the same weight through the same height but one does it faster than the other. Which motor has the most power?

• Two cherry pickers lifted the same weight, 75N, the same height, 5m. Cherry picker A Comparing two electric motors

• took 2 s and cherry picker B took 4s.

W (Joules) = f (Newtons) x s (metres)

P (Watts) =W (Joules) x t (seconds)

The formula for powerpower = energy transferred x time

P = Et • power, P, in watts, W• energy transferred, E,

in joules, J• time, t, in seconds, sThe energy

transferred is also called

the work done

The formula for powerpower = work done x time

P = Wt• power, P, in watts, W• time, t, in seconds, s• work done, W, in joules, JThe energy

transferred is also called

the work done

Level 1 exam question

Level 1 exam question

Level 1 exam question