Physics

Grade-9

Easy

Question

# An oven consumes 425 kWh of energy in order to provide 386 kWh of useful energy. What is its percent efficiency?

- 90%
- 91%
- 92%
- 93%

Hint:

- Efficiency (%) = (useful energy output ÷ energy input) × 100

## The correct answer is: 91%

- Efficiency (%) = (useful energy output ÷ energy input) × 100

### Related Questions to study

Physics

### Your heating system is 55 percent energy-efficient. What amount of energy would it consume to transform 9000 kWh into useful thermal energy for heating the house during the winter?

### Your heating system is 55 percent energy-efficient. What amount of energy would it consume to transform 9000 kWh into useful thermal energy for heating the house during the winter?

PhysicsGrade-9

Physics

### A television that is 83% efficient provides 6000 J of useful energy. How much energy does it consume?

### A television that is 83% efficient provides 6000 J of useful energy. How much energy does it consume?

PhysicsGrade-9

Physics

### Some homes are still heated by hot water boiler furnaces. The components of the system are an oil tank, a furnace, water pipes and radiators. The furnace burns the oil from the storage tank. The heat released is used to heat water which is then pumped to radiators throughout the house. A diagram is shown below.

If all the heat from the combustion was used to heat the water, the system would be 100% efficient. However, some heat is lost in the furnace exhaust and some is lost from the pipes delivering the water to the radiators.

One litre of oil delivers 48 000 kJ of energy. 7 600 kJ are lost to the exhaust, and 900 kJ are lost in transporting the hot water to the radiators. Determine the efficiency of this heating system.

### Some homes are still heated by hot water boiler furnaces. The components of the system are an oil tank, a furnace, water pipes and radiators. The furnace burns the oil from the storage tank. The heat released is used to heat water which is then pumped to radiators throughout the house. A diagram is shown below.

If all the heat from the combustion was used to heat the water, the system would be 100% efficient. However, some heat is lost in the furnace exhaust and some is lost from the pipes delivering the water to the radiators.

One litre of oil delivers 48 000 kJ of energy. 7 600 kJ are lost to the exhaust, and 900 kJ are lost in transporting the hot water to the radiators. Determine the efficiency of this heating system.

PhysicsGrade-9

Physics

### A simple diagram of a Hydro-Electric System is shown below

why all the energy from the water flowing into the turbine is not transformed into electrical energy.

### A simple diagram of a Hydro-Electric System is shown below

why all the energy from the water flowing into the turbine is not transformed into electrical energy.

PhysicsGrade-9

Physics

### An electrician installs patio lights in a back yard. Which of the following will decrease the efficiency of the wiring system to the back yard?

1- Bury the extension cord very deep down underground.

2- Use a short extension cord.

3- Use a long extension cord.

4- Use compact fluorescent light bulbs

### An electrician installs patio lights in a back yard. Which of the following will decrease the efficiency of the wiring system to the back yard?

1- Bury the extension cord very deep down underground.

2- Use a short extension cord.

3- Use a long extension cord.

4- Use compact fluorescent light bulbs

PhysicsGrade-9

Physics

### 20 joules of energy are transformed into light, how much energy is dissipated as heat out of 40J given in.

### 20 joules of energy are transformed into light, how much energy is dissipated as heat out of 40J given in.

PhysicsGrade-9

Physics

### Which glows brighter?

### Which glows brighter?

PhysicsGrade-9

Physics

### Total current is the sum of the current across each resistor in

### Total current is the sum of the current across each resistor in

PhysicsGrade-9

Physics

### Total current is the same across each resistance in

### Total current is the same across each resistance in

PhysicsGrade-9

Physics

### Your heating system is 45 percent energy efficient. The total useful output energy is 9000 kWh.

Changing the insulation would increase your house to 85 percent energy efficient. The cost to change the insulation is 131776 Rs. The cost of heating is 7 Rs/ kWh. How much time will it take to recover your investment?

### Your heating system is 45 percent energy efficient. The total useful output energy is 9000 kWh.

Changing the insulation would increase your house to 85 percent energy efficient. The cost to change the insulation is 131776 Rs. The cost of heating is 7 Rs/ kWh. How much time will it take to recover your investment?

PhysicsGrade-9

Physics

### A particular chemical process has an energy efficiency of only 3.00%. To complete this large-scale chemical process, 140,000 J of energy is input. What is the useful energy output of this process?

### A particular chemical process has an energy efficiency of only 3.00%. To complete this large-scale chemical process, 140,000 J of energy is input. What is the useful energy output of this process?

PhysicsGrade-9

Physics

### A construction worker puts 20 J of energy in to one strike of his hammer on the head of a nail. The energy transferred to the act driving the nail in to the wood is 8.0 J. What is his efficiency of hammering?

### A construction worker puts 20 J of energy in to one strike of his hammer on the head of a nail. The energy transferred to the act driving the nail in to the wood is 8.0 J. What is his efficiency of hammering?

PhysicsGrade-9

Physics

### A technician examines different electrical devices to determine the one that is the most energy efficient. While conducting a test, he notes that one of these devices consumes 650 000 J of energy and loses 315 000 J at the same time. What is the energy efficiency of this device?

### A technician examines different electrical devices to determine the one that is the most energy efficient. While conducting a test, he notes that one of these devices consumes 650 000 J of energy and loses 315 000 J at the same time. What is the energy efficiency of this device?

PhysicsGrade-9

Physics

### The table below has three different hairdryer models. Which is the least energy-efficient model?

### The table below has three different hairdryer models. Which is the least energy-efficient model?

PhysicsGrade-9

Physics

### An oven consumes 525 kWh of energy to provide 386 kWh of useful energy. What is its percentage efficiency?

### An oven consumes 525 kWh of energy to provide 386 kWh of useful energy. What is its percentage efficiency?

PhysicsGrade-9