Efficiency & Energy Resources Flashcards

All 23 cards in this deck

Why do mechanical processes that involve friction waste energy?

Friction causes a rise in temperature, so energy is dissipated by heating the surroundings.

What happens to energy that is dissipated in a system change?

It is stored in less useful ways, usually as thermal energy in the surroundings.

In an electric motor lifting a load, what is the useful energy transfer and what is the wasted energy transfer?

Useful: energy transferred to the gravitational store of the load.
Wasted: heating of the motor and surroundings (and sound).

How does lubrication reduce unwanted energy transfer in a gearbox?

Oil reduces friction between the moving parts, so less energy is wasted heating the surroundings.

How does thermal insulation in the walls of a house reduce unwanted energy transfer?

It has a low thermal conductivity, so energy is transferred out of the house more slowly.

What effect does increasing the thickness of a building's walls have on its rate of cooling?

Thicker walls give a slower rate of cooling.

True or false? A material with a higher thermal conductivity is the better insulator.

False. The better insulator has the lower thermal conductivity.

What is the equation for efficiency?

$\text{efficiency} = \dfrac{\text{useful energy transferred by the device}}{\text{total energy supplied to the device}}$ (× 100 for a percentage)

True or false? A device can have an efficiency greater than 1 (or more than 100%).

False. Useful energy can never be more than the total energy supplied, so efficiency is never above 1.

Name four non-renewable energy sources.

Coal, oil, natural gas and nuclear (uranium).

Name five renewable energy resources.

Wind, hydro-electricity, tides, the Sun (solar) and bio-fuel (biomass); also waves and geothermal.

Give two reasons for the trend of increasing use of renewable energy resources.

They never run out / are sustainable, and they do not produce carbon dioxide or greenhouse gases (except biomass), so they slow climate change.

Compared with fossil fuels, what are the main advantage and disadvantage of nuclear fuel?

Advantage: no carbon dioxide produced.
Disadvantage: radioactive waste is produced and there are safety concerns.

Which energy resources are mainly used for transport, and which are mainly used for generating electricity?

Transport: mostly non-renewables (petrol/diesel from oil), with some bio-fuel and electricity.
Electricity: fossil fuels, nuclear and renewables such as wind, solar and hydro.

True or false? Bio-fuel is a renewable resource.

True. New crops can be grown to replace those used, so it does not run out.

What is the difference between a non-renewable and a renewable energy resource?

A non-renewable resource will eventually run out; a renewable resource is replaced naturally, so it will never run out.

What are the main advantage and main disadvantage of using fossil fuels to generate electricity?

Advantage: reliable and relatively cheap — electricity can be generated whenever it is needed.
Disadvantage: burning them releases carbon dioxide, which adds to global warming.

What are the main advantage and main disadvantage of using wind turbines to generate electricity?

Advantage: they release no polluting gases while generating.
Disadvantage: unreliable — they generate nothing when the wind drops.

What are the main advantage and main disadvantage of using solar cells to generate electricity?

Advantage: no fuel is burned, so no polluting gases are released.
Disadvantage: they only generate electricity in daylight.

What are the main advantage and main disadvantage of using hydro-electric power to generate electricity?

Advantage: it can respond immediately when demand for electricity rises.
Disadvantage: the dam floods a valley, which badly damages the environment.

What are the main advantage and main disadvantage of using tidal barrages to generate electricity?

Advantage: reliable, because the times and heights of the tides can be predicted.
Disadvantage: the barrage alters the estuary, harming the habitats of the wildlife that live there.

Give three reasons why renewable energy resources are not used more widely.

Fossil fuels are cheaper and new renewable plants are expensive to build; some renewables are unreliable or can't increase output on demand; local people often oppose new sites such as wind farms.

What does the thermal conductivity of a material describe?

How easily energy passes through the material by heating.