Energy and Energy Resources Chp 1 part 2 Flashcards
What is useful energy?
Energy transferred to where it is wanted in the way that is desired.
What is wasted energy?
Energy not usually transferred as useful energy.
What happens to wasted energy?
It is dissipated
What is the most surprising example of waste energy?
Friction
What is dissipated energy?
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.
What would happen to energy transfer and changes to energy stores, to a gear box that is insulated so heat energy cannot be lost?
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.
What is the equation for input energy?
input energy (Joules) = useful output energy + energy wasted
What is the equation for the efficiency of energy transfer?
efficiency (Number or percentage) = useful output transferred by the device (J) / total input energy supplied to the device (J)
What does it mean for efficiency to have a limit?
That you can never put in more than 100% of what is given, so can never be more than 100% efficiency.
How do we reduce friction to increase efficiency?
Lubricate moving parts
How do we reduce the resistance of a wire/circuit and increase it’s efficiency?
Use wires with the least resistance
How do we reduce air resistance to increase efficiency?
Streamline the shapes of moving objects to reduce air resistance
Compare the useful energy output of a machine and the input energy supplied to the machine.
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.
What factors make machines less efficient?
Friction between moving parts, air resistance, electrical resistance and noise.
What is the useful energy and the waste energy of a lightbulb?
- Light emitted from the glowing filament
- Energy transfer from the filament heating the surroundings
What is the useful energy and the waste energy of a toaster?
- Heating bread
-Heating the toaster surrounding the air. Both are thermal.
What is the useful energy and the waste energy of a hairdryer?
- 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.
Where does the electricity supply for the home come from?
Electricity and gas or electricity and oil.
Why does a clockwork radio need to be wound up before it can be used?
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.
What is Power?
The rate of transfer of energy.
What is the equation for power?
P (w) = E (j) / T (s) also written as power (Watts) = energy transferred to an appliance (Joules) / time taken for the transfer (seconds)
How do we calculate the energy efficiency of an appliance? (Equation)
(useful power out / total power in) x 100%
How do we work out power wasted?
Total power input - useful power output
What is thermal conductivity?
The ability to conduct heat. The energy transfer of conduction through a material depends on its thermal conductivity.
What does insulation do to thermal conductivity?
Reduces it.
Compare high thermal conductivity to low thermal conductivity.
High thermal conductivity: Heat transfers quickly (e.g., metals).
Low thermal conductivity: Heat transfers slowly (e.g., insulators like wool or foam).
Why does a conductor have high thermal conductivity?
Because metals allow heat to move through them easily.
Why is a good thermal conductor often a good conductor of electricity?
Because both types of conduction rely on movement of free electrons.
Compare electrical and thermal conduction
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.
What makes a good insulator?
Low thermal conductivity
What is infrared radiation?
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.
What is Blackbody radiation?
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.
What happens to the infrared radiation of an object that becomes hotter?
It emits more infrared radiation, which is why we can see body heat more in hotter areas on a night vision camera.
When can an object emit radiation across a continuous range of wavelengths?
When it is at a constant temperature.
What happens when an object absorbs radiation faster than it emits radiation?
It gets hotter.
What affects the earth’s temperature?
Absorption of infrared radiation from the sun, the emission of radiation from the earth’s surface and atmosphere.
Explain how the earth heats up from infrared radiation.
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.
