Electrical energy and power - Physics form 5

Electrical energy and power

Physics form 5

Poll

How are you feeling today?

• Feeling good

• Meh

• Feeling sad / Worried

• Bad mood!

What to expect from this lesson?

• I can state the relationship between electrical energy (E), voltage (V), current (I) and time (t) in a formula.

• I can state the relationship between electrical power (P), voltage (V) and current (I) in a formula.

• I can calculate questions related to electrical energy and power.

• I can state what is power rating in electrical appliances.

• I can state a few ways to save electrical energy.

E = VIt

• A smartphone with 3.8 V and 450 mA in one hour usage consumes 6156 J of energy.

• A television with 220 V and 0.25 A in one hour usage consumes 198000 J of energy.

• 1 J = 1 W s

P = VI

• A rice cooker with 240 V and 3 A produces 720 W of power.

• Since V = IR, we can have P = (IR)(I) to P = I²R

• And with I = V/R, we can also have P = (V)(V/R) to P = V²/R

• SI unit for power is W (watt) or J s^-1

Quiz time!

There are 2 questions.

Fill in the Blank

The output power of a battery is 80 W. Determine the electrical energy supplied by the battery in 10 s.

Fill in the Blank

The output power of a battery is 80 W. Determine the electrical energy supplied by the battery in 2 hours.

How to calculate cost of electricity?

• 1 unit = 1 kW h

• Lets say the cost of 1 unit is 30 cents.

• A hand mixer with 300 W is operated for 30 minutes. So the cost of electricity = (0.3 kW)(0.5 h)(0.30 cents) = RM0.045

Quiz time!

There are 2 questions.

Fill in the Blank

The cost of electricity is 30 cents per unit. Calculate the cost of using 600 W LED television for 8 hours, in RM.

Fill in the Blank

The cost of electricity is 30 cents per unit. Calculate the cost of using 1 kW vacuum cleaner for half an hour, in RM.

Power rating

• Power rating simply describes how much power an electrical device use for its operation.

• High power does not necessarily mean more powerful devices.

• For example, a 40 W compact fluorescent lamp and a 12 W LED lamp produce the same brightness.

Energy efficiency label

• Power rating show us the estimated energy consumption of an electrical appliance based on a star rating system.

• 5 star indicates the appliance is the most energy-efficient while 1 star indicates the less energy-efficient.

• Usually the 5 star appliances is more expensive but it can save your money (electric bill) in the long run.

Quiz time!

There are 1 question and 1 poll!

Multiple Choice

Which one is the best to light up your house?

• Filament bulb

• LED light bulb

Poll

Poll:

What is the aspect that you think the most important when buying a new refrigerator?

• Price

• Design

• Energy efficiency

• Space

• Extra functions

Do you know that you can reduce the use of electrical energy and save more money?

Open Ended

List down at least five energy saving measures that you can do at home.

Congratulations!

You completed this lesson.