L5th Michaelmas Physics Mid-Term (Kinematics, Magnetism + Energy Sources)

What is a quantity?

Something that can be measured or represented with numbers

What is a scalar quantity?

A quantity that only has magnitude (size) but no direction

Give an example of a scalar quantity

Time, density, distance, energy, power, speed, temperature, mass

What is displacement?

Distance in a given direction

What is a vector quantity?

A quantity that has magnitude and direction

Give an example of a vector quantity

Velocity, force, displacement, acceleration, weight, momentum

What is the speed and velocity of an object moving in a circle?

Constant speed, constantly changing velocity

What is the average speed of a person walking?

1.5 m/s

What is the average speed of a person running?

3 m/s

What is the average speed of a person cycling?

6 m/s

What is the average wind speed?

5-20 m/s

What is the average speed of sound in air?

340 m/s

What is the average speed of a car in a built-up area?

13 m/s

What is the average speed of a car on the motorway?

30 m/s

What is the average speed of a train?

55 m/s

What is the average speed of a plane?

250 m/s

What is the average speed of a ferry?

15 m/s

What is acceleration?

The rate of change of velocity

What is the unit of acceleration?

m/s^2

What is the rough acceleration due to gravity for all objects in free fall?

10 m/s^2

What does the gradient on a distance-time graph represent?

Speed

What do the straight uphill sections on a distance-time graph represent?

Travelling at a steady speed

The steeper the distance-time graph, the _______?

The steeper the distance-time graph, the faster it is going

What do the flat sections on a distance-time graph represent?

The object is stationary (stopped)

What do the curves on a distance-time graph represent?

Acceleration or deceleration

What do the steepening curves on a distance-time graph represent

Acceleration

What do the levelling off curves on a distance-time graph represent?

Deceleration

What does the gradient of a velocity-time graph represent?

Acceleration

What do the flat sections of a velocity-time graph represent?

Steady speed

The steeper the velocity-time graph, the _____________?

The steeper the velocity-time graph, the greater the acceleration or deceleration

What do the uphill sections of a velocity-time graph represent?

Acceleration

What do the downhill sections of a velocity-time graph represent?

Deceleration

What do the curves of a velocity-time graph represent?

Changing acceleration

What does the area beneath a velocity-time graph represent?

Distance travelled

What is the needle of a compass?

A magnet which lines up with the Earth’s magnetic field

Why does the Earth have a magnetic field?

Its iron core acts like a giant magnet

Which metals are magnetic?

Iron, nickel and cobalt (and neodymium in some circumstances)

Is magnetism a contact or non-contact force?

Non-contact - objects don’t have to be touching to experience a force

What is a magnetic field?

A region of space in which a magnetic object experiences a force

What is the magnetic field like within a uniform field?

Same strength and direction everywhere

What is induced magnetism?

When a magnetic material is magnetised to become a magnet

Name an example of a use of induced (temporary) magnets?

Scrap yard magnets

How can you demagnetise an induced magnet?

Drop, hit or heat the object

What kind of magnetic field do electromagnets produce?

A temporary magnetic field

What is the motor effect?

When a current-carrying wire inside a permanent magnetic field experiences a force

Why does the wire experience a force as part of the motor effect?

There is a temporary magnetic field around the current-carrying wire which interacts with the permanent magnetic field

When do permanent magnets produce a magnetic field?

All the time

When do induced magnets produce a magnetic field?

When they’re in another external magnetic field

What does the “softness” of a material affect?

How quickly it loses its magnetism

Why are temporary magnetic materials magnetically “soft”?

Because they lose their magnetism fairly quickly

How can a magnetic field be represented?

Field diagrams

What is a field diagram?

A series of lines that show where a magnetic field exists and its direction

What direction do the arrows on magnetic field lines always point?

North to south

What do the direction of the field lines show?

The direction of the force a north pole would feel if it was placed in that location

The stronger the magnetic field at any point, the ______ the field lines are?

The stronger the magnetic field at any point, the closer together the field lines are

Where is the magnetic field strongest at on a bar magnet?

The poles of the magnet

What poles are uniform magnetic fields created between?

Two opposite magnetic poles

What will two like poles do to each other?

Repel each other

What will two unlike poles do to each other?

Attract each other

Is the force between a permanent and an induced magnet always attractive or repulsive?

Attractive

What angle does the wire have to be to the magnetic field to experience the full force of the motor effect?

90 degrees

What is the magnetic flux density?

How many field lines there are in a region

What does the magnetic flux density show?

The strength of the magnetic field

Give an example of a non-renewable energy source

Coal, oil, (natural) gas, nuclear fuels

What are fossil fuels?

Natural sources that form underground over millions of years that are typically burnt to provide energy

Give an example of a renewable energy source

Wind, tidal, hydroelectric, solar, bio-fuel

How much pollution do wind turbines produce?

None (except for a little bit when they’re manufactured)

What is a disadvantage of wind turbines?

They are considered an eyesore by some

How many wind turbines do you need to replace one coal-fired power station?

1500

Why are there problems with reliability for wind turbines?

There is no power when the wind stops and it is impossible to increase supply when there is extra demand (weather dependent)

What percentage of the time are wind turbines producing electricity (typically)?

70-85% of the time

How high are the initial costs of setting up wind turbines?

Quite high

What are the fuel costs and running costs of wind turbines?

No fuel costs and minimal running costs

How do solar cells generate electricity?

Directly from the Sun’s radiation

How much pollution do solar cells produce?

None

How high are the initial costs of setting up solar cells?

High

Give an example of a product that typically uses solar cells

Calculators, road signs, watches, satellites

What does generating electricity using hydroelectric power usually require?

The flooding of a valley by building a big dam

How much pollution do hydroelectric power stations produce?

None

What does the flooding of a valley due to hydroelectric power stations lead to?

Rotting vegetation (which releases methane and carbon dioxide) and possible loss of habitat (for both animals and humans)

What is an advantage of hydroelectric power stations that not many other renewable sources have?

They can provide an immediate response to an increase in demand for electricity and there is no problem with reliability except in times of drought

Give an example of how tides are used to generate electricity

Tidal barrages

What are tidal barrages?

Big dams built across river estuaries with turbines in them

How much pollution do tidal barrages produce?

None

What are bio-fuels created from?

Plant products or animal dung

Why are bio-fuels fairly reliable?

Crops take a relatively short time to grow and different crops can be grown all year round

How high is the cost to refine bio-fuels?

Very high

Why are bio-fuels considered carbon-neutral?

The plants that grow to produce the bio-fuel absorb carbon dioxide from the atmosphere when they are growing, then when they are burned, this carbon dioxide is released back into the atmosphere, so it has a neutral effect on atmospheric carbon dioxide levels

Give an example of a reason why bio-fuels may not be carbon neutral

Fossil fuels are often used in the transport of seeds and crops

Why is using animal dung as a bio-fuel an environmental problem?

Animals such as cows produce large amounts of methane over their lifetime

Give an advantage of using fossil fuels

They are cost-effect and reliable (there is enough fuel to meet current demand and power plants can respond quickly to changes in demand)

How much pollution do fossil fuels release

Lots of carbon dioxide

How does nuclear power work?

Nuclear fission of nuclear fuels such as uranium or plutonium releases the energy to heat water into steam which drives turbines

Why is nuclear power considered a “clean” resource?

It doesn’t cause the release of any harmful gases or other chemicals into the atmosphere

Name a disadvantage of nuclear fuels?

The nuclear waste produced is very dangerous and difficult to dispose of (because it stays highly radioactive for a long time)

Why is the overall cost of nuclear power high?

Due to the cost of the power station and final decommissioning

Name a disaster caused by nuclear power stations

Chernobyl 1986 or Fukushima 2011

Why has the electricity use of the UK hugely increased over the 20th century?

The population has increased and people have begun to use electricity for more things