Physics P1a

Question	Answer
Describe three ways that heat energy can be transferred.	Radiation - is the transfer of energy through infrared radiation (infrared radiation can be absorbed or emitted by any object) , conduction- in solids, or convection - in liquids or gases
True or false? An object that is cooler than its surroundings emits more radiation than it absorbs.	False - an object that is cooler than its surroundings absorbs more radiation than it emits (as it warms up)
Explain why solar hot water panels have a matt black surface.	Because dark matt surfaces absorb infrared radiation however light, shiny surfaces reflect it. Matt black surfaces also emit more at any given temperature.
Describe the arrangement and the movement of the particles in: A) solids B) Liquids C) Gases	A) Strong forces of attraction hold the particles closed together in a fixed arrangement, they vibrate as they don't have much energy. B) Weaker forces of attraction, particles are close together by move around each other, irregular arrangements, more energy than solids, move in random directions at low speeds C) almost no forces of attraction between particles, more energy than liquids and solids, free to move, travel in random directions at high speeds.
What is the name of the process where vibrating particles pass on their extra kinetic energy to neighbouring particles?	Conduction
Which type of heat transfer cant take place in solids?	Convection
Describe how the heat from the heater coils is transferred throughout the water in the kettle. What is this process called?	Conduction - heat energy is transferred from the heater coil to the water by conduction (particle collisions). The particles near the coil get more energy so they move faster. This means there is more distance between them, the water expands, becomes less dense. Hotter water moves above the cooler water. So therefor the hotter water moves the cooler water out of the way moving it closer to the coil, repeating the process as the hotter water cools.
How do the densities of liquids and gases change as you heat them?	A liquids and a gases densities decrease as they are heated because a liquid becomes a gas and a gas stays a gas but becomes lighter.
What happens to the particles of a gas as it turns into a liquid?	They slow down and lose kinetic energy, the attractive forces of the particles bring them closer together.
What is the name given to the process where a gas turns into a liquid?	Condensation
Why does evaporation have a cooling effect on a liquid?	because as the fastest particles evaporate so the average speed and the kinetic energy of the remaining particles decrease. This decrease in the average particle energy means the temperature of the remaining liquid falls.
Describe two features of a vacuum flask that make it good at keeping liquids hot.	1. the bottle is supported by an insolating foam that minimises heat conduction to or from the outer glass bottle 2. the glass bottle is double-walled with a vacuum between the walls so that all conduction and convection through the sides stops.
Do animals that live in hot climates have large or small ears? Give one reason why this might be an advantage in a hot climate.	They have large ears because it helps control heat transfer as it allows them to lose heat by radiation easily and keep cool.
if it costs £4000 to double-glaze your house and the double-glaze saves you £100 per year, calculate the payback time.	payback time = initial cost / annual saving Payback time = 4000/100 = 40 40 years
Name five ways to improve energy efficiency in the home. Explain how each improvement reduces the amount of heat loss.	Cavity wall insulation - foam squirted into the gap between the bricks stops convection currents being set up in the gap and radiation across the gap. The foam has air pockets in it so it helps reduce the heat by conduction Loft insulation - a thick layer of fibre glass wool laid out across the floor reduces conduction and radiation into the roof space from the ceiling. Draught proofing - strips of foam and plastic around doors and windows to stop draught of cold air blowing in i.e. they reduce heat loss due to convection Hot water tank jacket - lagging such as fibreglass wool reduces conduction and radiation Thick curtains - big bits of cloth over windows to reduce heat loss by conduction and radiation.
What can you tell from a materials U-value?	whether or not it is a good insulator. For example, if it is a good insulator the u- value will be low.
Would you expect copper or cotton wool to have a higher u-value?	Copper would have a higher u-value
What property of a material tells you how much energy it can store?	The specific heat capacity.
An ornament has a mass of 0.5kg. The ornament is made from a material which has a specific heat capacity of 1000j/kg degrees c. How much energy does it take to heat the ornament from 20 degrees to 200 degrees?	Energy transferred = mass x specific heat capacity x temperature change = 0.5 x 1000 x 180 = 90,000 J
Do heaters use materials that have high or low heat capacities?	High heat capacities so they can store loads of energy
Name nine types of energy and give an example of each.	1. Electrical energy - whenever a current flows 2. light energy - sun, light bulbs 3. sound energy - loudspeakers (anything noisy ) 4. Kinetic energy or movement energy - anything that's moving 5. nuclear energy - released from nuclear reactions only 6. Thermal energy or heat energy - flows from hot objects to colder ones 7. gravitational potential energy - anything that can fall 8. elastic potential energy - springs, elastic, rubber bands 9. chemical energy - foods, fuels, batteries
State the principle of conservation energy.	Energy can be transferred usefully from one form to another , stored or dissipated - but it can never be created or destroyed. Energy is only useful when it can be converted from one form to another.
List the energy transformations that occur in a battery-powered toy car.	Chemical energy to electrical and heat energy.
What is the useful energy delivered by a motor? In what form is energy wasted?	Kinetic energy and the waste Is heat.
What is the efficiency of a motor that converts 100 J of electrical energy into 70 J of useful kinetic energy?	Efficiency = useful energy out / total energy in = 70/100 = 0.7 0r 70%
What are the standard units of electrical energy?	Kilowatt-hours ( kWh)
calculate how many kWh of electrical energy are used by a 0.5 kW heater used for 15 minutes.	Energy = power x time = 0.5 x 15 = 30 J
Would a battery-powered radio or a clockwork radio be more suitable to use in rural Africa? why?	A clockwork radio would be better because it is completely free except from the initial price and is very good from the environment. Also, they do not have access to extra batteries whereas there is not extra items need other than to just wind it up.

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