Pressure Questions for IGCSE Physics

1 The diagram shows a simple mercury barometer.

On which diver is there the greatest pressure?

5 The air trapped in a cylinder by a piston is kept under pressure by a load, as shown in Fig. 4.1.

If atmospheric pressure increases, what happens to level X and to level Y?

2 A measured mass of gas is placed in a cylinder at atmospheric pressure and is then slowly compressed.

If the temperature of the gas does not change, what happens to the pressure of the gas? A It drops to zero. B It decreases, but not to zero. C It stays the same. D It increases.

(a) Describe how the pressure in the cylinder is caused by the air molecules. (b) The load is increased. (i) State what happens to the piston. (ii) State what happens to the pressure in the cylinder, and give a reason. what happens

6 Which diagram shows the child exerting least pressure on the ground?

3 The diagram shows an instrument used to measure gas pressure.

What is the instrument called? A ammeter B barometer C manometer D thermometer 4 The diagrams show two divers swimming in the sea and two divers swimming in fresh water. Sea water is more dense than fresh water.

7 A manometer is being used to measure the pressure of the gas inside a tank. A, B, C and D show the manometer at different times. At which time is the gas pressure inside the tank greatest?

8 Driving a car raises the temperature of the tyres. This causes the pressure of the air in the tyres to increase. Why is this? A Air molecules break up to form separate atoms. B Air molecules expand with the rise in temperature. C The force between the air molecules increases. D The speed of the air molecules increases

(a) The density of water is 1000 kg/m3 and the acceleration of free fall is 10 m/s2. Calculate the pressure that the water exerts on the diver. (b) The window in the diver’s helmet is 150 mm wide and 70 mm from top to bottom. Calculate the force that the water exerts on this window.

9 (a) A farmer has two vehicles with the same weight and the same number of wheels. Fig. 4.1 shows what the wheels on these two vehicles look like.

11 The diagram shows a simple mercury barometer. The barometer reading is hcm of mercury

Which vehicle should the farmer use when driving across his fields when the ground is very soft? Give your reasons. (b) (i) If you stepped on the point of a sharp nail with your bare foot, it would be extremely painful. Explain, in terms of pressure, why this is so. (ii) A person can lie on a bed of nail-points if there is a large number of nails. Explain why this is not extremely painful.

What is the pressure at S? A approximately zero B atmospheric pressure C atmospheric pressure + hcm of mercury D hcm of mercury 12 Two boys X and Y each have the same total weight and are standing on soft ground.

10 Fig. 2.1 shows a diver 50 m below the surface of the water.

Which boy is more likely to sink into the soft ground and why?

13 A student places his thumb firmly on the outlet of a bicycle pump, to stop the air coming out.

What happens to the pressure and to the volume of the trapped air as the pump handle is pushed in?

14 A balloon is inflated in a cold room. When the room becomes much warmer, the balloon becomes larger. How does the behaviour of the air molecules in the balloon explain this? A The molecules become larger. B The molecules evaporate. C The molecules move more quickly. D The molecules repel each other. 15 Liquid X has a density of 1010 kg / m3. Liquid Y has a density of 950 kg / m3. The liquids are poured into tubes as shown. Which tube has the greatest pressure on its base?

16 The diagram represents gas molecules contained in a cylinder. The piston is moved slowly downwards and the temperature of the gas stays the same.

Why does the pressure of the gas increase? A The molecules collide harder with the walls. B The molecules collide more often with the walls. C The molecules move more quickly. D The number of molecules increases. 17 (a) In Fig. 2.1, the sealed drum containing gas has a mercury manometer connected to it in order to indicate the gas pressure.

For convenience, gas pressure is often expressed in mm of mercury. The gas pressure is 781 mm of mercury and air pressure is 760 mm of mercury. (i) State the difference in height between levels A and B on the manometer. difference in height = ………….………..mm (ii) The temperature of the gas rises. State what happens to 1. the gas pressure, 2. the level A, 3. the level B. (b) The air in part (a) is also pressing on a large window pane in the wall of the room where the drum is situated. (i) State how the air pressure on the window pane compares with the air pressure on the mercury surface at B in Fig. 2.1. (ii) State how the force exerted by the air on the window pane compares with the force exerted by the air on the mercury surface at B.

18 Fig. 2.1 shows a reservoir that stores water.

(a) The valve in the exit pipe is closed. The density of water is 1000 kg/m3 and the acceleration of free fall is 10 m/s2. Calculate the pressure of the water acting on the closed valve in the exit pipe. (b) The cross-sectional area of the pipe is 0.5m2. Calculate the force exerted by the water on the closed valve. (c) The valve is then opened and water, originally at the surface of the reservoir, finally

flows out of the exit pipe. State the energy transformation of this water between the surface of the reservoir and the open end of the pipe.

22 An experiment is set up as shown.

19 A water manometer is used to measure the pressure of a gas supply to a house. It gives a reading of h cm of water.

What does the pressure gauge show as the air in the flask becomes hotter? A a steady pressure B a decrease in pressure C an increase in pressure D an increase and then a decrease in pressure Why is it better to use water rather than mercury in this manometer? A h would be too large if mercury were used. B h would be too small if mercury were used. C The tube would need to be narrower if mercury were used. D The tube would need to be wider if mercury were used.

23 (a) On a hot day, a child drinks all the water in a plastic bottle. She then screws the cap back tightly on the bottle, so that the bottle contains only air.

20 A farmer has two carts. The carts have the same weight, but one has four narrow wheels and the other has four wide wheels.

In rainy weather, which cart sinks less into soft ground, and why?

21 A measured mass of gas is placed in a cylinder at atmospheric pressure and is then slowly compressed.

The temperature of the gas does not change. What happens to the pressure of the gas? A It drops to zero. B It decreases, but not to zero. C It stays the same. D It increases.

She throws the bottle into a waste basket, where the Sun shines on it. After a while in the Sun’s rays, the air in the bottle is much hotter than before. (i) State what has happened to the pressure of the air in the bottle. (ii) In terms of the behaviour of the air molecules, explain your answer to (a)(i). (b) Also in the waste basket is a broken glass bottle containing a small quantity of water, as shown in Fig. 5.2.

As the Sun shines on it, the volume of water slowly decreases. (i) State the name of the process causing this decrease.

(ii) In terms of the effect of the Sun’s rays on the water molecules, explain your answer to (b)(i).

27 Fig. 3.1 shows a pond that is kept at a constant depth by a pressure-operated valve in the base.

24 The diagram shows a mercury barometer.

Which distance is used to calculate the pressure of the atmosphere? A 25 cm B 75 cm C 80 cm D 100 cm 11 Four blocks, each weighing 10 N, rest on a horizontal table. Which block applies the greatest pressure on the table?

25 (a) Fig. 3.1 shows two examples of footwear being worn by people of equal weight at a Winter Olympics competition.

Which footwear creates the greatest pressure below it, and why? (b) Drivers of high-sided vehicles, like the one in Fig. 3.2, are sometimes warned not to drive when it is very windy.

Suggest why they receive this warning. 26 Fig. 3.1 shows a pond that is kept at a constant depth by a pressure-operated valve in the base.

(a) The pond is kept at a depth of 2.0 m. The density of water is 1000 kg/m3. Calculate the water pressure on the valve. (b) The force required to open the valve is 50 N. The valve will open when the water depth reaches 2.0 m. Calculate the area of the valve. (c) The water supply is turned off and the valve is held open so that water drains out through the valve. State the energy changes of the water that occur as the depth of the water drops from 2.0 m to zero. 28 Fig. 5.1 shows a way of indicating the positions and direction of movement of some molecules in a gas at one instant.

(a) (i) Describe the movement of the molecules. (ii) Explain how the molecules exert a pressure on the container walls. (b) When the gas in the cylinder is heated, it pushes the piston further out of the cylinder. State what happens to (i) the average spacing of the molecules, (ii) the average speed of the molecules. (c) The gas shown in Fig. 5.1 is changed into a liquid and then into a solid by cooling. Compare the gaseous and solid states in terms of (i) the movement of the molecules, (ii) the average separation of the molecules. 29 (a) For a special parade, the guest of honour is to sit on a chair whilst the parade passes by. Unfortunately the ground beneath the chair is soft, so the parade organisers put the chair on a large flat board, as shown in Fig. 1.1.

Explain why the board prevents the chair from sinking into the ground. (b) At the parade, some air-filled balloons are used as decorations, as shown in Fig. 1.2.

(i) State what happens to the balloons when the Sun makes them hotter. (ii) In terms of molecules, explain your answer to (b)(i). (c) A pump is used to pump up the balloons in (b). A valve in the pump becomes blocked, as shown in Fig. 1.3.

(i) The piston of the pump is pushed in. State what happens to the pressure of the air trapped in the pump. (ii) In terms of molecules, explain your answer to (c)(i). 30 To prevent a cement mixer sinking into soft ground, the mixer is placed on a large flat board.

Why does this prevent the mixer sinking? A The large area decreases the pressure on the ground. B The large area increases the pressure on the ground. C The large area decreases the weight on the ground. D The large area increases the weight on the ground. 31 The diagram shows a simple mercury barometer.

The atmospheric pressure increases. Which distance increases? A VW B WY C XY D XZ 32 A pressure is measured using a manometer as shown in the diagram.

The water in the manometer is replaced with a liquid which is more dense. How does the value of h change? A It becomes zero. B It decreases, but not to zero. C It stays the same. D It increases. 32 A cylinder is filled with a gas and then sealed, so that the gas has a fixed volume.

The gas molecules are given energy so that their average speed increases. What happens to the pressure and to the temperature of the gas in the cylinder?

34 Fig. 2.1 shows a steam safety valve. When the pressure gets too high, the steam lifts the weight W and allows steam to escape.

33 (a) Fig. 6.1 shows how the pressure of the gas sealed in a container varies during a period of time. (a) Explain, in terms of moments of forces, how the valve works. (b) The moment of weight W about the pivot is 12 N m. The perpendicular distance of the line of action of the force of the steam on the valve from the pivot is 0.2 m. The area of the piston is 0.0003 m2. Calculate (i) the minimum steam force needed for the steam to escape, (ii) the minimum steam pressure for the steam to escape. Which of the following statements could explain this variation of pressure? Tick two statements.

35 The diagram shows a simple mercury barometer, used to measure atmospheric pressure.

(b) Fig. 6.2 shows some gas trapped in a cylinder with a movable piston. Atmospheric pressure increases. What happens to the level L and to the pressure at P?

The temperature of the gas is raised. (i) State what must happen to the piston, if anything, in order to keep the pressure of the gas constant. (ii) State your reasons for your answer to (b)(i).

36 The gas in a container is heated but is kept at constant volume. Why does the gas pressure increase? A The molecules expand. B The molecules increase in mass. C The molecules move further apart.

D The molecules move more rapidly. 37 Fig. 3.1 shows a simple mercury barometer, drawn 1/10 full size.

Which statement is correct? A The pressure at P is atmospheric pressure. B The pressure at P is nearly zero. C The pressure at Q is lower than the pressure at P. D The pressure at Q is nearly zero. 40 A brick with rectangular sides rests on a table.

(a) On Fig. 3.1, use your rule to make an appropriate measurement, and then use it to calculate the atmospheric pressure. (b) State what occupies the space in the tube above the mercury.

The brick is now turned so that it rests on the table on its smallest face.

12 A manometer is used to indicate the pressure in a steel vessel, as shown in the diagram.

What value does the liquid manometer give for the pressure in the vessel? A It is zero. B It is between zero and atmospheric pressure. C It is equal to atmospheric pressure. D It is greater than atmospheric pressure. 38 Four glass tanks contain water. In which tank is the pressure of the water on the base greatest?

39 The diagram shows a simple mercury barometer used to measure atmospheric pressure.

How has this change affected the force and the pressure exerted by the brick on the table?

41 The pressure of a fixed mass of gas in a cylinder is measured. The volume of the gas in the cylinder is then slowly decreased. Which graph could show the change of pressure of the gas during this process?

mercury in both tubes. Which labelled position on the right-hand tube could show the mercury level in that tube?

42 Fig. 6.1 shows two mercury barometers standing side by side. The right-hand diagram is incomplete. The space labelled X is a vacuum.

(a) On the left-hand barometer, carefully mark the distance that would have to be measured in order to find the value of the atmospheric pressure. [2] (b) A small quantity of air is introduced into X. (i) State what happens to the mercury level in the tube. (ii) In terms of the behaviour of the air molecules, explain your answer to (b)(i). (c) The space above the mercury in the righthand barometer is a vacuum. On Fig. 6.1, mark the level of the mercury surface in the tube. (d) The left-hand tube now has air above the mercury; the right-hand tube has a vacuum. Complete the table below, using words chosen from the following list, to indicate the effect of changing the external conditions. rises falls stays the same

43 The diagrams show two mercury barometers standing side by side. The right-hand diagram shows a tube of bigger diameter, but the diagram is incomplete. There is a vacuum above the

44 A student fills two containers with water (density 1.0 g / cm3) and two with oil (density 0.8 g / cm3), as shown in the diagrams. In which container is the pressure on the base the greatest?

45 A piston traps a certain mass of gas inside a cylinder. Initially the piston is halfway along the length of the cylinder. The piston is now moved towards the open end of the cylinder. The temperature of the gas remains constant.

How are the density and the pressure of the gas affected by moving the piston?

46 Fig. 4.1 shows a manometer, containing mercury, being used to monitor the pressure of a gas supply.

The mercury in the manometer is replaced with a liquid which is less dense. How does the value of h change? A It becomes zero. B It decreases, but not to zero. C It stays the same. D It increases.

(a) Using the scale on Fig. 4.1, find the vertical difference between the two mercury levels. (b) What is the value of the excess pressure of the gas supply, measured in millimetres of mercury? (c) The atmospheric pressure is 750 mm of mercury. Calculate the actual pressure of the gas supply. (d) The gas pressure now decreases by 20 mm of mercury. On Fig. 4.1, mark the new positions of the two mercury levels.

49 (a) Fig. 4.1 shows end views of the walls built by two bricklayers.

47 (a) A man squeezes a pin between his thumb and finger, as shown in Fig. 6.1.

Which wall is the least likely to sink into the soil, and why? (b) Fig. 4.2 shows two horizontal squares P and Q.

The finger exerts a force of 84 N on the pinhead. The pinhead has an area of 6.0 10–5 m2. (i) Calculate the pressure exerted by the finger on the pinhead. (ii) State the value of the force exerted by the pin on the thumb. (iii) Explain why the pin causes more pain in the man’s thumb than in his finger. 48 The pressure of a gas is measured using a manometer as shown in the diagram.

The atmosphere is pressing down on both P and Q. (i) Name two quantities that would need to be known in order to calculate the atmospheric pressure on square P. (ii) The area of P is four times that of Q. Complete the following sentences.

1. The atmospheric pressure on P is ……………………………… the atmospheric pressure on Q. 2. The force of the atmosphere on P is ……………………………… the force of the atmosphere on Q.

at constant temperature, and the other shows how the pressure varies with temperature at constant volume. The pressure axis has been labelled in each case.

4 What is a simple mercury barometer designed to measure? A the pressure beneath a liquid B the pressure of a gas supply C the pressure of car tyres D the pressure of the atmosphere 50 A sealed gas cylinder is left outside on a hot, sunny day. What happens to the average speed of the molecules and to the pressure of the gas in the cylinder as the temperature rises?

(i) On the appropriate graphs, label one horizontal axis “ volume / m3 ” and the other horizontal axis “ temperature / °C ”. (ii) On one of the graphs, mark, with the letter X, the pressure of the gas at the ice point. 53 During a period of hot weather, the atmospheric pressure on the pond in Fig. 3.1 remains constant. Water evaporates from the pond, so that the depth h decreases.

51 The diagram shows two mercury barometers. Barometer 1 is measuring atmospheric pressure on day 1. Barometer 2 is measuring atmospheric pressure on day 2.

Which statement is true? A The atmospheric pressure on day 1 is less than the atmospheric pressure on day 2. B The atmospheric pressure on day 1 is the same as the atmospheric pressure on day 2. C The pressure at point X is less than the pressure at point Y. D The pressure at point X is the same as the pressure at point Y. 52 A fixed amount of dry gas is exerting a pressure on its container. (a) In terms of molecules, explain what causes the pressure. (b) One of the sketch graphs in Fig. 2.1 shows how the pressure of the gas varies with volume

(a) Study the diagram and state, giving your reason, what happens during this hot period to (i) the force of the air on the surface of the pond, (ii) the pressure at the bottom of the pond. (b) On a certain day, the pond is 12 m deep. (i) Water has a density of 1000 kg / m3. Calculate the pressure at the bottom of the pond due to the water. (ii) Atmospheric pressure on that day is 1.0 × 105 Pa. Calculate the total pressure at the bottom of the pond. (iii) A bubble of gas is released from the mud at the bottom of the pond. Its initial volume is 0.5 cm3. Ignoring any temperature differences in the water, calculate the volume of the bubble as it reaches the surface. (iv) In fact, the temperature of the water is greater at the top than at the bottom of the pond. Comment on the bubble volume you have calculated in (b)(iii).

54 Fig. 5.1 shows a gas contained in a cylinder enclosed by a piston.

pressure gauge, is 300 kPa. The area of crosssection of the cylinder is 0.12 m2. (a) (i) Describe the motion of the molecules of the gas. (ii) Explain how the molecules exert a force on the walls of the cylinder. (iii) Calculate the force exerted by the gas on the piston. (b) The piston is moved so that the new length of cylinder occupied by the gas is 50 cm. The temperature of the gas is unchanged. (i) Calculate the new pressure of the gas. pressure = (ii) Explain, in terms of the behaviour of the molecules, why the pressure has changed.

(b) The value of h taken using this barometer is 0.73 m. The density of mercury is 13 600 kg / m3. Calculate the value of the atmospheric pressure suggested by this measurement. Use g = 10 m / s2. (c) Standard atmospheric pressure is 0.76 m of mercury. Suggest a reason why the value of h in (b) is lower than this.

55 A chair is placed on protective cups to prevent damage to the carpet underneath it.

4 A sealed balloon containing some helium gas is released and rises into the upper atmosphere. As the balloon rises the temperature of the helium falls and the balloon expands. Explain, in terms of atoms, (a) the effect of the fall in temperature on the helium pressure, (b) the effect of the expansion of the balloon on the helium pressure.

How do the cups change the area of contact with the carpet and the pressure on it?

4 A soldier wears boots, each having an area of 0.016 m2 in contact with the ground. The soldier weighs 720 N. (a) (i) Write down the equation that is used to find the pressure exerted by the soldier on the ground. (ii) Calculate the pressure exerted by the soldier when he is standing to attention, with both boots on the ground. (b) The soldier is crossing a sandy desert. Explain, stating the relevant Physics, why this soldier is at an advantage over another soldier who has the same weight but smaller feet. (c) The soldier’s unit is sent to a cold country, and on one occasion he has to cross a frozen lake. Suggest one way that the soldier can reduce the risk of the ice breaking under his weight.

56 (a) Complete Fig. 4.1 to show a simple mercury barometer. Insert the correct labels in the boxes. Label with the letter h the measurement required to calculate the pressure of the atmosphere.

2 Fig. 2.1 shows a simple mercury barometer alongside a mercury manometer that contains some trapped gas.

Which distance is used to calculate the pressure of the atmosphere? A 25 cm B 75 cm C 80 cm D 100 cm 3 Fig. 3.1 shows a manometer being used to measure the pressure of some gas in a container. The container is connected to the manometer by a length of rubber tubing.

From Fig. 2.1 find (a) the pressure of the atmosphere, (b) the pressure of the trapped gas. (c) The atmospheric pressure increases. State what happens to the levels of mercury in the manometer. left-hand level right-hand level 4 Fig. 4.1 represents part of the hydraulic braking system of a car.

The force F1 of the driver’s foot on the brake pedal moves piston X. The space between pistons X and Y is filled with oil which cannot be compressed. The force F2 exerted by the oil moves piston Y. This force is applied to the brake mechanism in the wheels of the car. The area of cross-section of piston X is 4.8 cm2. (a) The force F1 is 90 N. Calculate the pressure exerted on the oil by piston X. (b) The pressure on piston Y is the same as the pressure applied by piston X. Explain why the force F2 is greater than the force F1. (c) Piston Y moves a smaller distance than piston X. Explain why. (d) Suggest why the braking system does not work properly if the oil contains bubbles of air. 8 The diagram shows a mercury barometer.

(a) State whether the pressure of the gas in the container is greater than, the same as, or less than the pressure of the atmosphere. (b) From Fig. 3.1, deduce the difference between the gas pressure and the atmospheric pressure. mercury (c) The atmospheric pressure is 752 mm of mercury. Calculate the actual pressure of the gas in the container. (d) State how the vertical height difference of the two mercury surfaces changes, if at all, if a mercury manometer made from a narrower tube is used. 4 (a) Fig. 4.1 shows some gas contained in a cylinder by a heavy piston. The piston can move up and down in the cylinder with negligible friction.

There is a small increase in the pressure of the atmosphere above the piston. (i) On Fig. 4.1, draw a possible new position for the lower face of the piston. (ii) Explain, in terms of the molecules of the gas and the molecules of the atmosphere, your answer to (a)(i). (b) The pressure of the atmosphere above the piston returns to its original value, and the piston returns to its original position, as shown in Fig. 4.2.

The gas, piston and cylinder are now heated to a much higher temperature. (i) On Fig. 4.2, draw a possible new position for the lower face of the piston. (ii) Explain, in terms of the molecules of the gas and the molecules of the atmosphere, your answer to (b)(i).

IGCSE PHYSICS ON 2002 TO ON 2012