IGS Ph Efficiency

A very efficient device ...

• ... transfers a very small proportion of the total energy transferred as waste energy.

• ... transfers a very big proportion of the total energy transferred as waste energy.

• ... works very well & is very effective.

How much energy is wasted?

• 100 J

• 75 J

• 50 J

• 25 J

How can you tell that the waste energy must be 25 joules?

• Energy is conserved.

• Energy allows work to be done.

• Energy is a scalar quantity.

What is the efficiency of the device shown?

• 100 %

• 25 %

• 75 %

If the efficiency of the device increased, what would happen to the numbers?

• The "100 %" would increase.

• The "25 %" would increase.

• The "75 %" would increase.

• The "25 %" would decrease.

• The "75 %" would decrease.

How would you calculate the efficiency of this device?

Use the equation in the box to calculate the efficiency of the device.

Choose the right answer.

• 0.86

A device has an efficiency of 0.65 (65 %).

Calculate the useful output energy when the total energy transferred is 100 J.

• 100 J

• 35 J

• 65 J

• 95 J

200 J is supplied to a device.

The device has an efficiency of 0.30 (30 %).

Calculate the useful output energy.

• 30 J

• 60 J

• 120 J

• 15 J