**Electrical Energy**

Electrical appliances are handy because we can use them simply by flicking a switch

Electrical appliances are rated by their power in Watts (W).

Power is the rate at which energy is transferred in different forms.

1 Watt of power = 1 Joule / 1 second or W = J / s

The Wattage or 'Power Rating' of an appliance tells us how many joules of electrical energy is being given to the appliance over a given time.

Joules of energy given to an appliance = Joules of energy transferred into different forms by the appliance (Law of conservation of energy).

Power Rating of an appliance does not give us an indication of how efficient an appliance is.

Electrical appliances are handy because we can use them simply by flicking a switch

Electrical appliances are rated by their power in Watts (W).

Power is the rate at which energy is transferred in different forms.

1 Watt of power = 1 Joule / 1 second or W = J / s

The Wattage or 'Power Rating' of an appliance tells us how many joules of electrical energy is being given to the appliance over a given time.

Joules of energy given to an appliance = Joules of energy transferred into different forms by the appliance (Law of conservation of energy).

Power Rating of an appliance does not give us an indication of how efficient an appliance is.

**Since power is the rate of doing work, or rate at which energy is transferred, efficiency can also be shown as:**

% Electrical efficiency = 100 x useful power out / total power in

% Electrical efficiency = 100 x useful power out / total power in

Although energy is usually measured in joules, other units of energy are also used.

Although energy is usually measured in joules, other units of energy are also used.

**E.g. We talk about energy in food in terms of**

__C__alories written with a capital C (1__C__alorie = 1000 calories = 4200 joules)**Energy used by electrical appliances is measured in kilowatt hours, kWh (1 kWh = 3600,000 joules = 3600 kJ)**

**1 kWh is the amount of energy supplied over 1 h to an electrical appliance which uses 1 kW of power.**