Test 10 + Thermal

Question 1

State the two conditions necessary for the helicopter to remain in equilibrium.

Answer 1

no resultant force
no resultant moment

Question 2

Explain, in terms of forces, the changes in motion which occur from when the parachutist leaves the hot-air balloon until the parachute opens.

Answer 2

Initially, the parachutist accelerates downwards due to his weight. At first, air resistance has little effect.

As velocity increases, air resistance increases. Acceleration decreases then stops.

He reaches a constant speed called terminal velocity when air resistance is equal to his weight.

Question 3

As the student catches the ball, she moves her hands backwards.
Explain the effect of this action on the student’s hands.

Answer 3

The ball has a longer time of impact and exerts a smaller force on her hand.

Question 4

Explain why this way of moving across the ice is safer than walking. Use your understanding of pressure in your answer.

Answer 4

Weight is spread over a larger area. P=F/A. Force remains the same, so pressure is lower and ice is less likely to crack.

Question 5

The temperature of a fixed mass of gas at constant volume is decreased.
State and explain, in terms of particles, how the pressure of the gas changes.

Answer 5

Particles collide into the wall less frequently. Particles collide with smaller force and have smaller momentum. Pressure decreases.

Question 6

Explain what is meant by the term absolute zero. Refer to particles in your answer.

Answer 6

Temperature at which particles have the least kinetic energy. It is the lowest possible temperature.

Question 7

Suggest one reason why the time calculated is the minimum time needed to increase the temperature of the air in the room from 16.0°C to 20.0°C.

Answer 7

 (thermal) energy is transferred to furniture / walls / objects (in the room)
 (thermal) energy is transferred through windows / doors / floor / ceiling / from the room

Question 8

State the main methods of thermal energy transfer from the room to outside which are reduced by a double-glazed window.

Answer 8

Conduction and convection.

Question 9

What is thermal conduction?

Answer 9

the transfer of thermal energy by vibrations of molecules

Question 10

What is convection?

Answer 10

the transfer of thermal energy through a material by the movement of the material itself

Question 11

What can you say about transferring heat by radiation?

Answer 11

• does not involve the movement of particles
• does not need a medium

Question 12

Calculating speed of light in a material?

Answer 12

n (refractive index of oil) = speed of light in air/ speed of light in oil

Question 13

Draw four lines to show the electric field and its direction of the negatively charged sphere.

Answer 13

equally-spaced lines outside sphere, touching sphere, pointing towards sphere

Question 14

All the cells are reversed.
1. State and explain the change in current in R1. (a diode is involved)

Answer 14

No current in R1 because diode is in the wrong direction and allows current to flow in one direction

Question 15

State two safety precautions taken when moving, using or storing radioactive sources in a laboratory.

Answer 15

 limit time of exposure
 store sources in lead boxes
 keep distance from sources
 avoid contact OR use tongs OR wear gloves

Question 16

State the equation that defines the average orbital speed v of a planet. State the meaning of any symbols you use.

Answer 16

v=2πr/T
r = (average) radius of the orbit AND T = (orbital) period

Question 17

Suggest why countries that are a significant distance from the Equator experience significant
temperature variation throughout the year.

Answer 17

rays from Sun strike the country at different angles through the year

Question 18

Fill in the gaps in the paragraph about a star much more massive than the Sun.

The stage that follows the stable state in the life cycle of the star is the …………….. stage.

It then explodes as a supernova to form a ………………….. , this leaves behind a
………………….. or a ……………..

Answer 18

The stage that follows the stable state in the life cycle of the star is the
(red supergiant) stage.

It then explodes as a supernova to form a (nebula) , this leaves behind a (neutron star) or a (black hole).

Question 19

A galaxy is moving away from the Earth with a speed of 33000km/ s.
The value of the Hubble constant is 2.2 × 10–18 per second.

Calculate the distance from the galaxy to the Earth. Give your answer in light-years.

Answer 19

Calculate as normal. Remember to multiply Hubble’s constant by 9.5 x 10^15 m, because that’s the distance of one light-year.

Question 20

Explain conduction in non-metals.

Answer 20

The temperature difference between the two ends, causes thermal energy to flow along the rod.

Particles of the hot end vibrate more than those at the other end. As the atoms vibrate, they collide with their neighbours, and so share their energy with the neighbouring atoms.

Atoms with a lot of energy end up with less and.. The collisions gradually transfer energy from the hot end to the cold end.

Question 21

Explain conduction in metals.

Answer 21

Contain electrons which are free to move. They carry electric current. They gain and carry thermal energy as they get hot and move through a metal. Energy is transferred from a region of high temperature to a region of low temperature.

Carry electric current

Question 22

Explain the troubles of conduction in fluids.

Answer 22

Liquids can conduct thermal energy because the particles are in close contact with each other. Vibrations are not passed on as easily as in solids because particles are free to move.

Gas particles are very spread out so they are very poor conductors of thermal energy.

Question 23

Which of the states of matter can transfer thermal energy by convection?

Answer 23

gas and liquids (fluids)

particles are in fixed positions so they cannot flow

Question 24

What is a convection current?

Answer 24

the transfer of thermal energy by the motion of a fluid

Question 25

An object hotter than its environment..

Answer 25

radiates more energy per second than it absorbs and so will cool down

Question 26

An object cooler than its environment..

Answer 26

absorbs more energy per second than it radiates until it reaches the temperature of its environment

Question 27

An object with a constant temperature..

Answer 27

absorbs thermal energy at the sam erate it radiates energy

Question 28

What can be said about the rate at which thermal energy is emitted by an object with a large surface area?

Answer 28

emits at a faster rate

Question 29

Infrared radiation can also pass through..

Answer 29

transparent materials such as air.

Question 30

(Of a house) How to prevent thermal transfer by convection?

Answer 30

thick curtains and drought excluders, double and triple glazed windows, foam or rockwool in wall cavity

Question 31

(Of a house) How to prevent thermal energy transfer by conduction?

Answer 31

loft and underfloor insulating materials, double and triple glazed windows, cavity walls

Question 32

What are vacuum flasks used for?

Answer 32

• keeping drinks hot or cold
• used to store liquid nitrogen and helium at low temps to be used in eg: body scanners in hospitals
  -medical uses such as storing frozen embryos for IVF treatment

Question 33

What materials are usually used in a flask and why?

Answer 33

Glass is a good insulator, steel for strength,
silver coating on glass reflect infrared radiation,
stopper prevents losses by convection and evaporation
Air is removed between the gap of the double walls to create a vacuum and reduce losses by conduction and convection

Question 34

Explain the cooling of a hot car engine:

Answer 34

Water has a high specific heat capacity and flows around the block to absorb energy.
Convection current flows and a pump is used to speed up the flow.
Radiator has metal fins , so energy is conducted to all parts of the radiator.
The fins have a large sa and are black to increase the rate of thermal energy radiation.

Question 35

The bonfire

Answer 35

Almost entirely due to radiation. Air is a bad conductor. Convection will heat the air above the fire.

Question 36

What causes global warming?

Answer 36

The Earth and its atmosphere are absorbing more infrared radiation than they emit. Convection currents explain the origins of wind and ocean currents.
There is evidence that the pattern of ocean currents is changing and this is perhaps a consequence of global warming.

Question 37

Explain why a non-metal conducts thermal energy less well than a metal.

Answer 37

no free electrons

Question 38

Explain, in terms of particles, why gases are poor thermal conductors compared to non-metal solids.

Answer 38

further apart and fewer collisions

Question 39

Explain how convection causes the temperature of all the water in the beaker to decrease.

Answer 39

Density of water increases. This cold water sinks and warm water rises to replace it.

Question 40

Explain one other advantage of keeping the surface of the pan shiny.

Answer 40

The shiny surface is a poor emitter of radiation, and so reduces thermal energy losses