Lesson 12

• Physics
• Middelbare school
• vwo
• Leerjaar 3

Chapter 3 — Energy

This lesson

• The practical
  
• Discussing the homework
  
• Quiz
  

The practical

Q​w​​=U⋅A⋅ΔT

Q=c⋅m⋅ΔT

E=P⋅T

P=U⋅I

η=​E​tot​​​​E​used​​​​⋅100÷

From Chapter 1

Paragraph 3

Discussing the homework

Exercise 1

Someone uses their laptop for 40 minutes. Their laptop has a power of 250 watt. In this time the laptop loses energy through things like heat and generating sound. In these 40 minutes the laptop loses 216000 joules to this. Calculate the efficiency of this laptop.

Exercise 2

When the sun is shining brightly, the incoming irradiation at an alpine hut is 1000 W/m2. A solar panel with a surface area of 1.8 m2 supplies a maximum power of 288 W.

Calculate the efficiency of this solar panel.

Exercise 3

A motorcycle has an efficiency of 27%. The motor cycle uses 7,4 liter of petrol to drive about 110 kilometer. There is 31500000 joules in one liter of petrol. Calculate how much energy in joules went into making the motor move.

On the right you see a system that functions similar to a calorie meter. In what ways does this system loose energy?

A

The point of the system is to heat the water. All energy that goes in is used to heat the water. Therefor no energy is lost.

B

The system looses energy through the open top of the beaker.

On the right you see a system that functions similar to a calorie meter. In what ways does this system loose energy?

A

The point of the system is to heat the water. All energy that goes in is used to heat the water. Therefor no energy is lost.

B

The system looses energy through the open top of the beaker.

On the right you see a system that functions similar to a calorie meter. Through which methods of heat transfer does this system loose energy?

A

Convection

B

Conduction

C

Radiation

D

All three of the previous options

On the right you see a system that functions similar to a calorie meter. Through which methods of heat transfer does this system loose energy?

A

Convection

B

Conduction

C

Radiation

D

All three of the previous options

What is heat at a molecular level?

A

The exchange of electrons between molecules.

B

The amount of energy molecules are charged up with.

C

It is impossible to describe.

D

The vibration of molecules (internal kinetic energy).

What is heat at a molecular level?

A

The exchange of electrons between molecules.

B

The amount of energy molecules are charged up with.

C

It is impossible to describe.

D

The vibration of molecules (internal kinetic energy).

Specific heat capacity  is the amount of energy needed to heat up 1 gram of a substance 1 ºC.  

• Nitrogen gas has a specific heat capacity of 1.040 J/kg•ºC
  
• Neon gas has a specific heat capacity of 1.0301 J/kg•ºC

Which gas requires less energy to heat up?

A

Nitrogen gas.

B

Neon gas.

Specific heat capacity  is the amount of energy needed to heat up 1 gram of a substance 1 ºC.  

• Nitrogen gas has a specific heat capacity of 1.040 J/kg•ºC
  
• Neon gas has a specific heat capacity of 1.0301 J/kg•ºC

Which gas requires les energy to heat up?

A

Nitrogen gas.

B

Neon gas.

What is the primary mode of heat transfer that warms up earths surface?

A

Convection.

B

Conduction.

C

Radiation.

D

All three of the previous options.

What is the primary mode of heat transfer that warms up earths surface?

A

Convection.

B

Conduction.

C

Radiation.

D

All three of the previous options.

When an ice cube is place in a warm room. Which of the following options best describes the heat flow?

A

Heat flows from the room into the ice cube.

B

Heat flows out of the ice cube into the room. 

C

Heat flows equally in both directions.

D

There is no heat flow between the ice cube and the room.

When an ice cube is place in a warm room. Which of the following options best describes the heat flow?

A

Heat flows from the room into the ice cube.

B

Heat flows out of the ice cube into the room. 

C

Heat flows equally in both directions.

D

There is no heat flow between the ice cube and the room.

When someone is building a house, what is the relationship between the surface area of house and the amount of heat energy that flows out of the house?

A

A larger surface area means they will have more insulation which means less heat will flow out.

B

A smaller surface area means more heat will flow out per square meter.

C

The large the surface area of the house the more heat will flow out.

D

None of the previous options.

Q​w​​=U⋅A⋅ΔT

When someone is building a house, what is the relationship between the surface area of house and the amount of heat energy that flows out of the house?

A

A larger surface area means they will have more insulation which means less heat will flow out.

B

A smaller surface area means more heat will flow out per square meter.

C

The large the surface area of the house the more heat will flow out.

D

None of the previous options.

Q​w​​=U⋅A⋅ΔT