Energy and Energy Resources Chp 1 part 2

Question 1

What is useful energy?

Answer 1

Energy transferred to where it is wanted in the way that is desired.

Question 2

What is wasted energy?

Answer 2

Energy not usually transferred as useful energy.

Question 3

What happens to wasted energy?

Answer 3

It is dissipated

Question 4

What is the most surprising example of waste energy?

Answer 4

Friction

Question 5

What is dissipated energy?

Answer 5

Energy that spreads out to the surroundings, eg. sound and heat (sometimes heat is not waste if it is desired). Even useful energy can eventually dissipate.

Question 6

What would happen to energy transfer and changes to energy stores, to a gear box that is insulated so heat energy cannot be lost?

Answer 6

In a gearbox that is insulated, no heat energy can escape to the surroundings. When energy is transferred to the gearbox (usually as mechanical energy from moving parts), some energy is usually wasted as heat due to friction. However, with insulation, this heat energy remains inside and the gear box becomes hot to touch, as it builds up thermal energy store.

Question 7

What is the equation for input energy?

Answer 7

input energy (Joules) = useful output energy + energy wasted

Question 8

What is the equation for the efficiency of energy transfer?

Answer 8

efficiency (Number or percentage) = useful output transferred by the device (J) / total input energy supplied to the device (J)

Question 9

What does it mean for efficiency to have a limit?

Answer 9

That you can never put in more than 100% of what is given, so can never be more than 100% efficiency.

Question 10

How do we reduce friction to increase efficiency?

Answer 10

Lubricate moving parts

Question 11

How do we reduce the resistance of a wire/circuit and increase it’s efficiency?

Answer 11

Use wires with the least resistance

Question 12

How do we reduce air resistance to increase efficiency?

Answer 12

Streamline the shapes of moving objects to reduce air resistance

Question 13

Compare the useful energy output of a machine and the input energy supplied to the machine.

Answer 13

Input energy: Energy supplied to the machine.
Useful energy output: Energy that the machine uses effectively for its intended purpose.
Energy loss: Unwanted energy, like heat or sound.
The efficiency of a machine shows how much of the input energy is converted into useful energy.

Question 14

What factors make machines less efficient?

Answer 14

Friction between moving parts, air resistance, electrical resistance and noise.

Question 15

What is the useful energy and the waste energy of a lightbulb?

Answer 15

• Light emitted from the glowing filament
• Energy transfer from the filament heating the surroundings

Question 16

What is the useful energy and the waste energy of a toaster?

Answer 16

• Heating bread
  -Heating the toaster surrounding the air. Both are thermal.

Question 17

What is the useful energy and the waste energy of a hairdryer?

Answer 17

• Kinetic energy of the fan moving the air and thermal energy from the heater filament.
• Sound of the fan motor
  -Thermal energy heating the hairdryer itself.

Question 18

Where does the electricity supply for the home come from?

Answer 18

Electricity and gas or electricity and oil.

Question 19

Why does a clockwork radio need to be wound up before it can be used?

Answer 19

Because the handle winds a spring, increasing it’s elastic potential energy store, which is transferred to kinetic energy store turning a small electric (electricity) generator inside the radio.

Question 20

What is Power?

Answer 20

The rate of transfer of energy.

Question 21

What is the equation for power?

Answer 21

P (w) = E (j) / T (s) also written as power (Watts) = energy transferred to an appliance (Joules) / time taken for the transfer (seconds)

Question 22

How do we calculate the energy efficiency of an appliance? (Equation)

Answer 22

(useful power out / total power in) x 100%

Question 23

How do we work out power wasted?

Answer 23

Total power input - useful power output

Question 24

What is thermal conductivity?

Answer 24

The ability to conduct heat. The energy transfer of conduction through a material depends on its thermal conductivity.

Question 25

What does insulation do to thermal conductivity?

Answer 25

Reduces it.

Question 26

Compare high thermal conductivity to low thermal conductivity.

Answer 26

High thermal conductivity: Heat transfers quickly (e.g., metals). Low thermal conductivity: Heat transfers slowly (e.g., insulators like wool or foam).

Question 27

Why does a conductor have high thermal conductivity?

Answer 27

Because metals allow heat to move through them easily.

Question 28

Why is a good thermal conductor often a good conductor of electricity?

Answer 28

Because both types of conduction rely on movement of free electrons.

Question 29

Compare electrical and thermal conduction

Answer 29

Electrical conduction is the movement of electric charges (usually electrons) through a material, creating an electric current. Thermal conduction is the transfer of heat energy through a material, mainly due to the movement of vibrating particles and free electrons.

Question 30

What makes a good insulator?

Answer 30

Low thermal conductivity

Question 31

What is infrared radiation?

Answer 31

Infrared radiation is a type of electromagnetic wave that carries heat energy. It is emitted by all objects and is part of the electromagnetic spectrum, with wavelengths longer than visible light but shorter than microwaves. Infrared radiation can travel through space and does not require particles to transfer heat.

Question 32

What is Blackbody radiation?

Answer 32

Blackbody radiation is radiation emitted by a body (an object) that absorbs all of the radiation incident on it. The body (object) that can absorb all of the radiation is called a black body.

Question 33

What happens to the infrared radiation of an object that becomes hotter?

Answer 33

It emits more infrared radiation, which is why we can see body heat more in hotter areas on a night vision camera.

Question 34

When can an object emit radiation across a continuous range of wavelengths?

Answer 34

When it is at a constant temperature.

Question 35

What happens when an object absorbs radiation faster than it emits radiation?

Answer 35

It gets hotter.

Question 36

What affects the earth's temperature?

Answer 36

Absorption of infrared radiation from the sun, the emission of radiation from the earth's surface and atmosphere.

Question 37

Explain how the earth heats up from infrared radiation.

Answer 37

Infrared radiation from sun warms ground, Ground emits longer wavelength infrared radiation. CO2 molecules absorb and reemit this infrared radiation back to the ground - stops heat escaping into space.