Flashcard 1
Q: When a device or object undergoes an energy change, what happens to the input energy?
A: When a device or object undergoes an energy change, some of the energy that is input is transferred usefully, while some of it is dissipated or wasted by being transferred to other, less useful energy stores.
Flashcard 2
Q: Why are devices considered useful in terms of energy transfers?
A: Useful devices are considered useful because they are able to transfer energy from one energy store to another.
Flashcard 3
Q: What usually happens to some of the input energy in most energy transfers?
A: In most energy transfers, some of the input energy is usually wasted by being transferred to a useless energy store, which is usually a thermal energy store.
Flashcard 4
Q: What is meant by the efficiency of a device?
A: The efficiency of a device is a measure of how good the device is at transferring input energy into useful output energy.
Flashcard 5
Q: How is efficiency defined in terms of energy transfers?
A: Efficiency is the proportion (or ratio) of the energy supplied to a device that is transferred in useful ways.
Flashcard 6
Q: What does it mean if a device is very efficient?
A: A very efficient device wastes very little of its input energy, meaning that most of the energy supplied to it is transferred into useful energy stores.
Flashcard 7
Q: What does it mean if a device is very inefficient?
A: A very inefficient device wastes most of its input energy, meaning that only a small proportion of the supplied energy is transferred usefully.
Flashcard 8
Q: How does the amount of wasted energy affect the efficiency of a device?
A: The less energy that is wasted by being transferred to useless energy stores, the more efficient the device is said to be.
Flashcard 9
Q: What is the equation for calculating efficiency using energy?
A: The efficiency of a device can be calculated using the equation:
Efficiency = Useful output energy transfer (J) ÷ Total input energy transfer (J).
Flashcard 10
Q: What units must be used when calculating efficiency using energy?
A: When calculating efficiency using energy, both the useful energy transferred and the total energy supplied must be measured in joules (J).
Flashcard 11
Q: How can efficiency be calculated using power instead of energy?
A: Efficiency can also be calculated using power with the equation:
Efficiency = Useful power output (W) ÷ Total power input (W).
Flashcard 12
Q: Why can power be used to calculate efficiency?
A: Power can be used to calculate efficiency because power is equal to the useful energy transferred per second.
Flashcard 13
Q: What units must be used when calculating efficiency using power?
A: When calculating efficiency using power, both the useful power transferred and the total power supplied must be measured in watts (W).
Flashcard 14
Q: How can efficiency be expressed as a percentage?
A: Efficiency can be converted into a percentage by multiplying the decimal value of efficiency by 100.
Flashcard 15
Q: What is the equation for percentage efficiency using energy values?
A: Percentage efficiency can be calculated using the equation:
Percentage efficiency = (Useful energy transferred ÷ Total energy supplied) × 100.
Flashcard 16
Q: What is the equation for percentage efficiency using power values?
A: Percentage efficiency can be calculated using the equation:
Percentage efficiency = (Useful power transferred ÷ Total power supplied) × 100.
Flashcard 17
Q: Can the efficiency of a device ever be greater than 1 or greater than 100%?
A: No. It is not possible for a device to have an efficiency greater than 1 (or 100%). This would mean that more energy is being transferred out than was supplied, which would imply that energy is being created.
Flashcard 18
Q: Why is it impossible for a device to have an efficiency greater than 100%?
A: An efficiency greater than 100% would mean that more energy is being transferred than is being supplied, which would imply that energy is being created. This would break the law of conservation of energy.
Flashcard 19
Q: Why do devices waste energy?
A: Devices waste energy for various reasons including friction between moving parts, electrical resistance, air resistance, and the production of unwanted sound energy.
Flashcard 20
Q: What usually happens to energy that is wasted by devices?
A: Most wasted energy is transferred to thermal energy stores and dissipated into the surroundings.
Flashcard 21
Q: What types of processes commonly cause energy to be wasted in devices?
A: Energy in devices is commonly wasted due to friction between moving parts, electrical resistance, air resistance, and the production of sound.
Flashcard 22
Q: How can the efficiency of a device be improved?
A: The efficiency of a device can be improved by reducing wasted energy transfers so that a greater proportion of the input energy is transferred usefully.
Flashcard 23
Q: What is one method used to reduce wasted energy due to friction in machines?
A: Lubrication can be used to reduce the friction between moving parts in a machine, which reduces energy wasted as heat and improves efficiency.
Flashcard 24
Q: What are three design methods that can improve the efficiency of energy transfers?
A: The efficiency of energy transfers can be improved by insulating objects, lubricating moving parts, or making objects more streamlined.
Flashcard 25
Q: How does insulation improve efficiency?
A: Insulation improves efficiency by reducing the transfer of thermal energy to the surroundings, which reduces wasted energy.
Flashcard 26
Q: How does streamlining improve efficiency?
A: Streamlining reduces air resistance acting on an object, which reduces energy wasted overcoming drag and improves efficiency.
Flashcard 27
Q: What is meant by energy being dissipated?
A: Energy being dissipated means that it spreads out into the surroundings, usually as thermal energy, making it less useful for doing further work.
Flashcard 28
Q: In most devices, is the useful energy output equal to the total energy input?
A: No. In most devices the useful energy output is not equal to the total energy input because some energy is always wasted, usually transferred to thermal energy stores.
Flashcard 29
Q: Are any devices usually close to 100% efficient?
A: Electric heaters are usually close to 100% efficient because all of the energy from the electrostatic energy store of the electricity is transferred into thermal energy stores, which is the intended useful output.
Flashcard 30
Q: What ultimately happens to all energy transfers over time?
A: Ultimately, all energy ends up being transferred to thermal energy stores. For example, energy used by devices like electric drills may initially transfer to several different energy stores, but it quickly ends up as thermal energy in the surroundings.
Flashcard 31
Q: Example calculation: If a light bulb receives 200 J of energy and only 28 J is transferred usefully, how is its efficiency calculated?
A: The efficiency is calculated using:
Efficiency = Useful energy transferred ÷ Total energy supplied
Efficiency = 28 ÷ 200
Efficiency = 0.14.
Flashcard 32
Q: In the light bulb example where efficiency = 0.14, what is the percentage efficiency?
A: The percentage efficiency is calculated as:
Percentage efficiency = 0.14 × 100 = 14%.
Flashcard 33
Q: Why is the light bulb in the example considered inefficient?
A: The light bulb is considered inefficient because most of the energy supplied is not transferred usefully as light. Instead, most of the energy is dissipated as infrared radiation, with only 14% transferred usefully as light radiation.
Source 1: Efficiency
When a device or object is going through an energy change, some of the energy that is inputted is TRANSFERRED USEFULLY and some is DISSIPATED or wasted.
Efficiency is a ratio of the amount of useful energy that’s given out to the total amount of energy that was originally put in. The equation for this is: Efficiency = Useful Output Energy Transfer (J) / Total Input Energy Transfer (J). You can also rewrite the equation using power instead of energy to give you: Efficiency = Useful Power Output (W) / Total Power Input (W). ||| You can convert efficiency into percentages by multiplying by 100. ||| Improving Efficiency:
The efficiency of a device can be improved by REDUCING wasted energy transfers.
They waste energy mainly due to:
- Friction between their moving parts
- Air resistance
- Electrical resistance
- Sound
Most of these lead to THERMAL energy being dissipated into the SURROUNDINGS. If you can minimise these, you can IMPROVE the EFFICIENCY of a device. ////////// Source 2: Efficiency:
Devices are designed to waste as little energy as possible. This means that as much of the input energy as possible should be transferred into useful energy stores.
How good a device is at transferring energy input to useful energy output is called
efficiency.
A very efficient device will waste very little of its input energy.
A very inefficient device will waste most of its input energy.
The efficiency of a device is the proportion of the energy supplied that is transferred in useful ways. The efficiency can be calculated as a decimal or a percentage, using the equations: efficiency = useful energy transferred / total energy supplied
percentage efficiency = efficiency x 100
(percentage efficiency = useful energy transferred / total energy supplied x 100). This is when both useful energy transferred and total energy supplied are measured in joules (J). ||| Example Question:
The energy supplied to a light bulb is 200 J. A total of 28 J of this is usefully transferred. How efficient is the light bulb?
efficiency = useful energy transferred / total energy supplied
efficiency = 28 / 200
efficiency = 0.14
percentage efficiency = efficiency x 100
percentage efficiency = 0.14 x 100
percentage efficiency = 14%
The light bulb is not very efficient since most of the energy supplied is not transferred usefully. Most of the energy is dissipated as infrared radiation and only 14% is transferred usefully as light radiation. ||| Efficiency and power:
As power is equal to useful energy transferred per second, another way to calculate efficiency is to use the formula: efficiency = useful power transferred / total power supplied
percentage efficiency = efficiency x 100. This is when both useful power transferred and total power supplied are measured in watts (W). ||| It is not possible to have an efficiency of greater than 1 or efficiency percentage of 100%. This would mean that more energy is being transferred than is being supplied, which would mean that energy is being created. This would break the law of conservation of energy. ||| Wasted energy:
Devices waste energy for various reasons including friction between their moving parts, electrical resistance, and unwanted sound energy.
Devices can be made more efficient by reducing the energy that they waste or dissipate to the surroundings. One example is lubrication being used to reduce the friction between moving parts of a machine. /////////// Source 3: Efficiency: Most Energy Transfers Involve Some Waste Energy:
1) Useful devices are only useful because they can transfer energy from one store to another.
2) As you’ll probably have gathered by now, some of the input energy is usually wasted by being
transferred to a useless energy store - usually a thermal energy store.
3) The less energy that is ‘wasted’ in this energy store, the more efficient the device is said to be.
4) You can improve the efficiency of energy transfers by insulating objects, lubricating them or making them more streamlined.
5) The efficiency for any energy transfer can be worked out using this equation:
Efficiency = Useful output energy transfer / Total input energy transfer
6) You might not know the energy inputs and outputs of a device, but you can still
calculate its efficiency as long as you know the power input and output:
Efficiency = Useful power output / Total power input [Note that you can give efficiency as a
decimal or you can multiply your answer by 100 to get a percentage, i.e. 0.75 or 75%.] ||| Useful Energy Output Isn’t Usually Equal to Total Energy Input:
1) For any given example you can talk about the types of energy being input and output, but remember: NO device is 100% efficient and the wasted energy is usually transferred to useless thermal energy stores.
2) Electric heaters are the exception to this. They’re usually 100% efficient because all the energy in the electrostatic energy store is transferred to “useful” thermal energy stores.
3) Ultimately, all energy ends up transferred to thermal energy stores. For example, if you use an electric drill, its energy transfers to lots of different energy stores, but quickly ends up all in thermal energy stores.
Flashcard 1
Q: When a device or object undergoes an energy change
what happens to the input energy?
A: When a device or object undergoes an energy change
some of the energy that is input is transferred usefully
Flashcard 2
Q: Why are devices considered useful in terms of energy transfers?
A: Useful devices are considered useful because they are able to transfer energy from one energy store to another.
Flashcard 3
Q: What usually happens to some of the input energy in most energy transfers?
A: In most energy transfers
some of the input energy is usually wasted by being transferred to a useless energy store
Flashcard 4
Q: What is meant by the efficiency of a device?
A: The efficiency of a device is a measure of how good the device is at transferring input energy into useful output energy.
Flashcard 5
Q: How is efficiency defined in terms of energy transfers?
A: Efficiency is the proportion (or ratio) of the energy supplied to a device that is transferred in useful ways.
Flashcard 6
Q: What does it mean if a device is very efficient?
A: A very efficient device wastes very little of its input energy
meaning that most of the energy supplied to it is transferred into useful energy stores.
Flashcard 7
Q: What does it mean if a device is very inefficient?
A: A very inefficient device wastes most of its input energy
meaning that only a small proportion of the supplied energy is transferred usefully.
Flashcard 8
Q: How does the amount of wasted energy affect the efficiency of a device?
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Energy Stores and Transfers, Open and Closed Systems36
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Examples of Energy Transfers, Energy Flow Diagrams13
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Calculation of Energy Changes, Conservation of Energy11
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Energy Dissipation, Reducing Unwated Energy Transfers in the Home13
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Conduction and Convection112
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Specific Heat Capacity, Intro to Thermal Conductivity22
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Required Practical: Specific Heat Capacity20
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Power124
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Required Practical: Investigating Insulation121
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Efficiency108
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Types of Energy Resources290
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Trends and Uses of Energy Resources, Energy for Transport and Heating246
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Charge and Current82
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Current, Potential Difference & Resistance58
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Required Practical: Investigating Resistance89
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Resistors and I-V Graphs132
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Required Practical: I-V Graphs99
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Series and Parallel Circuits55
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Direct and Alternating Current31
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Mains Electricity78
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Electrical Power25
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Electrical Energy Transfers and Power Ratings71
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The National Grid84
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Static Electricity and Sparks77
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Electric Fields and Sparks75
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Density - Intro13
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Required Practical: Density17
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States of Matter36
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Internal Energy35
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Specific Latent Heat, Heating & Cooling Graphs (and recap of Internal Energy)36
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Particle Motion in Gases, Gas Pressure & Temp, Boyle's Law, Work Done on Gases41
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Atomic Structure, Radioactive Decay, Types of Radiation, Intro to G-M Tube75
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Nuclear Equations, Half Life, Contamination, Irradiation, Peer Reviewing79
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Background Radiation, Correct Count-Rate, Uses and Risks of Radiation45
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Nuclear Fission and Fusion97
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Scalars and Vectors24
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Contact and Non-Contact Forces71
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Gravity, Weight & Centre of Mass97
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Resultant Forces, Scale Drawings, & Components of a Force113
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Work Done and Its Energy Transfers53
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Forces and Elasticity112
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Required Practical: Force and Extension118
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Moments, Levers and Gears101
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Pressure in Fluids118
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Upthrust and Atmospheric Pressure67
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Distance and Displacement17
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Speed and Velocity25
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Distance-Time Graphs24
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Acceleration106
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Velocity-Time Graphs61
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Terminal Velocity121
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Newton's First Law and Inertia61
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Newton's Second Law and Inertial Mass51
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Newton's Third Law73
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Required Practical: Force, Mass and Acceleration137
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Stopping Distance and How Braking Works131
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Momentum and Changes in Momentum104
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Vehicle Safety Features40
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Transverse & Longitudinal Waves36
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Wave Period & Speed, Measuring the Speed of Sound in Air23
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Required Practical: Measuring Waves in a Ripple Tank19
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Required Practical: Measuring Waves on a String9
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Sound Waves and Human Hearing101
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Using Ultrasound for Imaging and Detection70
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Using Seismic Waves for Exploration81
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Intro to Electromagnetic Waves, Intro to Visible Light92
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Uses of Radio Waves91
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Uses of Microwaves25
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Uses of Infrared Radiation33
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Uses of Visible Light21
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Uses of Ultraviolet Radiation25
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Uses of X-Rays and Gamma Rays27
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Dangers of Electromagnetic Waves63
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Visible Light and Colour Filters137
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Required Practical: Investigating Infrared Radiation75
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Reflection and Refraction114
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Specular and Diffuse Reflection61
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Required Practical: Reflection and Refraction119
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Lenses and Ray Diagrams153
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Black Body Radiation and Earth’s Temperature169
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Magnetism and Types of Magnets28
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Magnetic Fields30
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Electromagnetism, The Right Hand Grip Rule and Solenoids40
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The Motor Effect55
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Fleming's Left Hand Rule41
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Electric Motors and Loudspeakers25
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Induced Potential, The Generator Effect and Microphones52
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Transformers and their Equations137
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Our Solar System and Orbital Motion184
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The Life Cycle of Stars100
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Red Shift and The Big Bang81
