CSEC Physics - 04 Energy / Temperature

What is the correct unit for energy?

• meters (m)

• Newtons (N)

• kilogram meters per second (kg m/s)

• Joules (J)

Complete the statement about the principal of Conservation of Energy.

Energy can be changed for one form to another but the total amount of energy

• always increases

• does not change

• always decreases

• varies according to the reaction

A battery releases 100J of energy to a lamp. The lamp releases 80J of energy as light but it also releases heat energy. How much heat energy is released?

• 180J

• 160J

• 20J

• 360J

Answer explanation

total energy input = 100

light output = 80

100J - 80J = 20J

that means that 20 J is left as heat

A battery releases 200J of energy to a lamp.

the energy is converted to heat and light.

50kJ is given out as heat. How much is released as Light?

• 100J

• 150J

• 200J

• 250J

Answer explanation

energy released 200J

energy as heat = 50kJ

200J - 50J = 150J

A torch battery releases 50J of energy as heat and 240J as light, What is the total energy released from the battery?

• 250J

• 280J

• 290J

• 300J

Answer explanation

heat energy output = 50J

light energy = 240J

50J + 240J = 290J

total energy released

The % energy efficiency of an appliance is

In a filament bulb the electrical power input is 40W and the light (Useful) energy output is 4W. What is the % efficiency?

• 1%

• 0.1%

• 10%

• 4%

In a modern low-energy bulb,

the electrical power input is 12W and the Light (useful) power output is 4W.

What is the energy efficiency of this bulb?

• 3%

• 25.5%

• 30%

• 33.3

Look at the last two questions Suggest why modern bulbs are more efficient? (There is more than one correct answer)

• They do not need as big an energy input

• They are not as bright

• There is less wasted energy

• They release less heat.

What is the Formula to calculate energy transfer for Kinetic Energy?

• E_k=1/2 mv²

• 1/2mv=k

• Em²⁼1/2^k

• EK² =2mv

Answer explanation

Kinetic energy is directly proportional to the mass of the object and to the square of its velocity:

K.E. = 1/2 m v².