Energy

1) What is Energy ?
Energy is the ability to do work.
Energy/Work Done (joules) = Power (watts) x Time (secs)
If units are kJ and or minutes they must be converted first.

2) What units are used for Energy transfer ?
Joules (J)
Kilojoules (kJ) - all food is measured in kJ
Kilowatt-hours (kWh)

3) Calculate the energy transferred by a 1.5 kW remote control car used for 1 hour.
Energy Transferred = Power (watts) x Time (secs)
Energy = 1500 x 3600
Energy = 5,400,000
Energy Transferred = Power (kW) x Time (hours)
Energy = 1.5 kWh

4) What are the eight different ways that energy can be stored ?
Kinetic - (movement) anything that moves has energy.
Elastic - anything stretched (eg springs, rubber bands)
Chemical - anything that can release energy by a chemical reaction (eg batteries, food, fuel)
Thermal - anything that is hot
Gravitational - anything in a gravitational field, the higher the object the more energy
Magnetic - two magnets attract or repel (north/south)
Electrostatic - two electric charges attract or repel (positive/negative), static electricity
Nuclear - involves splitting or fusing atoms

5) Can energy be used up ?
Energy is not destroyed, it is just transferred and conserved.
Energy is only useful when it is transferred.
When energy is transferred some of it will be wasted, typically by some form of heating.

6) What is Potential Energy ?
This is the energy that is stored in an object because of its position, stresses within itself, its electric charge or other factors.
Examples include: gravitational, elastic, magnetic, chemical, electrostatic, nuclear

7) Can you describe Energy Transfer ?
Energy can be transferred by doing work.
Energy can be transferred from one object to another.
Energy can be transferred between the different energy stores of the same object (eg kinetic to thermal)

8) What is a Closed System ?
This is an object where energy (or matter) cannot leave or enter.
The total amount of energy in a closed system remains constant.

9) Can you give some examples of energy transfer ?
Dropping an object - the object moves through the gravitational field.
   energy moves from Gravitational to Kinetic
   energy is transferred Mechanically (using the gravitational force)
Throwing a ball -
   energy moves from Chemical to Kinetic
   energy is transferred Mechanically (using a force)
Burning wood -
   energy moves from Chemical to Thermal
   energy is transferred by Heating
Stretching a Spring -
   energy moves from Elastic to Kinetic
   energy is transferred Mechanically

10) If you move an object (mechanically using a force) where is the energy transferred to ?
The energy required to move the object is transferred to the objects Kinetic energy store.

11) What is the formula for Kinetic Energy ?
Anything that is moving has kinetic energy, measured in Joules.
How much energy depends on the mass and the speed of the object.
E(k) = 1/2mv2
m = mass (kg), v = speed (m/s)

12) What is the formula for Gravitational Energy ?
How much energy depends on the mass, height and strength of the gravitational field.
E(g) = mgh
m = mass (kg), g = field strength (N/Kg), h = height (m)

13) What is the formula for Elastic Energy ?
E(e) = 1/2ke2
k = spring constant (N/m), e = extension (m)

14) What are the different ways that energy can be transferred ?
Radiation - (using waves) a vibration where matter does not move.
Mechanically - (using forces) when a force makes matter move (push, pull, stretch, squash)
Electrically - when electric charges moves around an electric circuit because of potential difference
Heating - (conduction, convection) when two objects are at different temperatures. Energy is transferred from the hotter to the cooler

15) If energy is transferred using Heating what is Thermal Equilibrium ?
Thermal energy will continue to be transferred until both objects reach the same temperature.
When the objects are the same temperature they have reached thermal equilibrium.

16) Can you describe Radiation ?
All objects send out invisible waves called radiation to their surroundings.
Two objects do not have to be touching for energy to be transferred using radiation.

17) We can be divide radiation into two categories, what are the two categories ?
Non-Ionising Radiation - (low frequency) A low-energy radiation that can pass through the body without being absorbed.
Ionising Radiation - (high frequency) They remove electrons from atoms to create positive ions. These waves can interact directly with a DNA molecule's atoms and prevent them from reproducing. Ultraviolet waves (found naturally in sunlight), X-rays and gamma rays

18) What are the different types of Radiation ?
All radiation can travel through solid objects, air and even vacuums.
Electromagnetic - These have no mass or charge. Synchronized oscillation of electric and magnetic fields. All transverse waves. All travel at very high speeds.
Alpha - when an alpha particle (2 protons & 2 neutrons) is emitted from the nucleus
Beta - when an electron is released by the nucleus
Neutrons - when a particle that has no charge is present in the nucleus of an atom

19) What is the Electromagnetic Spectrum ?
This is a list of the seven different groups of waves that make up Electromagnetic Radiation, with lowest frequency first (highest wavelength first)
Roman Men Invented Very Unusual Xray Glasses
Radio waves
These are waves with the lowest frequency in the electromagnetic spectrum
Microwaves
These are waves of the electromagnetic spectrum that can be used for heating or communicating
Infared waves
These are used for remote controls and heaters
Visible light
These are used for optical fibres and photography
Ultraviolet light
These can harm the human body, causes skin to age prematurely and increase the risk of skin cancer, used by sunbeds.
X-rays
These can harm the human body, These waves are not transmitted through bones.
Gamma rays
These can harm the human body, cause ionisation inside cells. This damage leads to the cells dying.

20) Do all Electromagnet Waves have the same wavelength ?
No.

21) What does the Radiation Dose tell you ?
This is a measure of the risk of harm to human body tissue when exposed to radiation.
It is measured in Sieverts (Sv)

22) Which group of electromagnetic waves has the shortest wavelength ?
Gamma rays have the shortest wavelength
Radio waves have the longest wavelength

23) Can you describe Conduction ?
Occurs mainly in solids
When an object is heated the particles have more energy and this energy is transferred when two objects are touching.
The particles vibrate more and collide with each other. These collisions cause energy to be transferred between the particles.
Energy is transferred to the Thermal energy store.
Thermal conductivity is a measure of how quickly energy is transferred with conduction.

24) Can you describe Convection ?
Occurs mainly in liquids and gases
Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy.
The particles can already move around in liquids and gases, but they move faster and space between the individual particles increases.
The density of the heated area will decrease.
radiators work by using convection in a gas.They heat the air near the radiator, reducing its density and making it rise.
lava lamps work by using convection in a liquid

25) What does the Specific Heat Capacity of an object tell us about Thermal Energy ?
It indicates how easy (or hard) it is to heat up an object.
This is the amount of energy needed to raise the temperature of 1Kg of a substance by 1 degree celcius.
The higher the SHC the more energy is needed to increase its temperature.

26) What are the units for Specific Heat Capacity ?
J/Kg oC

27) What is the formula for Thermal Heat Capacity ?
Change in Thermal Energy (J) = Mass (kg) x Specific Heat Capacity x Temperature Change (oC)

28) What is the Specific Latent Heat of Fusion ?
This is the amount of energy released/required when 1 kg changes stage between solid and liquid with no temperature change.

29) What is the Specific Latent Heat of Vaporisation ?
This is the amount of energy released/required when 1 kg changes stage between gas and liquid with no temperature change.

30) What are the units for Specific Latent Heat ?
J/Kg

31) What is Movement ?
The change in position of an object.

32) What is Motion ?
The action or process of "moving" or "changing" place or position.

33) How can the efficiency of energy transfer be calculated ?
Efficiency = Useful Output Energy / Total Input energy
The efficiency of energy transfer can be improved by insulating objects, lubricating or by streamlining.

34) The energy resources available on Earth can be divided into two categories, what are the two categories ?
Non-Renewable - Coal, Oil, Gas
Renewable - Sun, Wind, Water Waves, Water Tides, Hydro-electric, Biofuel, Geothermal

Energy Questions

35) In an experiment, a heater is used to heat a beaker of water.
The energy transferred and the temperature are recorded.
140kJ of energy is transferred in 12 minutes.
Calculate the average power transferred to the heater ?

Energy Transferred = Power(watts) x Time(secs) 
Power = Energy Transferred / Time 
Power = 140000 / (12 x 60) 
Power = 190 watts 

36) 85kJ of energy is transferred to the thermal store of the water.
Calculate the efficiency of this transfer ?

Efficiency = Useful Power Output / Total Power Output 
Efficiency = 85 / 140 
Efficiency = 0.6071 
Efficiency = 61% 

37) Identify two sources of uncertainty in the experiement ?
water changes in mass as it evaporates
random uncertainty in data logged
thermal energy dissipated from the water to the environment
delay in temperature of the water reaching equilibrium through the water

38) Would the time taken for the water to boil increase or decrease if the energy transfer was more efficient ?
The time taken would decrease.

39) Discuss some of the factors that an energy company would need to consider before deciding how to provide an energy supply to a new community ?
Environment concerns
fossil fuels emit carbon and other pollutants, contributing to global warming
renewable resources have less impact although there are carbon emissions from biofuels
Availability
non renewable are finite and will run out eventually
nuclear fuels are more plentiful and will not run out in the near future
renewable resources are plentiful
Reliability
some resources (Solar. Wind) do not generate electricity constantly, there are too many variables
so these would require energy storage

40) Someone does a bungee jump from a bridge
The original length of the bungee cord is 25 metres.
Its maximum extension during the jump is 18 metres.
The mass of the jumper is 65kg
Describe how the energy stores of the bungee jumper change at the different points ?
Before the jump
All the jumpers energy is stored as gravitational potential energy
During the jump
Energy is transferred between gravitational potential energy to kinetic energy
After the cord has become taut, but not at its full extension
The gravitational and kinetic energy are transfered to elastic potential energy in the cord
At the cords full extension
All the jumpers gravitational potential energy has been transferred to elastic potential energy

41) What are the equations for gravitational potential energy and elastic potential energy ?

Gravitational Potential Energy = Mass x Gravitational Field Strength x Change in Height 
Elastic Potential Energy = 0.5 x Spring Constant x Extension(squared) 

42) Show that the spring contant is 170N/m
Use g = 9.8 N/Kg