2024_AQA A-Level Physics Paper 3 Section B Engineering Physic (Merged Question Paper and Marking Scheme)

2024_AQA A-Level Physics Paper 3 Section B Engineering Physic (Merged Question Paper and Marking Scheme) Monday 17 June 2024 2 Do not write outside the IB/M/Jun24/7408/3BC There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED 3 A-Level Physics: Paper 3 Section B – Engineering Physics: Exam sections Section B of Paper 3 focuses on Engineering Physics, which explores how physics principles are applied in the design and operation of engineering systems. This section covers key concepts in mechanics, materials, thermodynamics, and electricity, with a focus on practical applications. 1. Mechanics and Materials:  Forces and Motion: o Understand the concepts of force, torque, and moment of inertia, and how they relate to rotational motion. o Be able to apply Newton’s Laws to solve problems involving motion and forces, including friction, air resistance, and tension in cables.  Stress and Strain: o Study the behavior of materials under stress, including concepts like tensile stress, shear stress, and compressive stress. o Understand strain (the deformation due to stress) and the relationship between stress and strain in materials. o Be familiar with Young’s Modulus, which is the ratio of stress to strain, and how it measures a material’s stiffness. o Review elastic and plastic deformation, and the concept of the yield point.  Materials Properties: 2. Thermodynamics and Heat Transfer:  Laws of Thermodynamics: o Understand the first law of thermodynamics (energy conservation), second law of thermodynamics (entropy), and third law (absolute zero of entropy). o Apply these principles to solve problems involving heat engines, refrigerators, and heat pumps.  Heat Transfer: o Understand the modes of heat transfer: conduction, convection, and radiation, and how these processes occur in different materials and systems. o Be able to apply the heat conduction equation and the concepts of thermal resistance in composite materials. 3. Fluid Mechanics:  Fluid Statics: 6. Key Concepts to Revise:  Mechanics of materials: Understand material behavior under stress and the concepts of strain, Young’s Modulus, and elasticity.  Thermodynamics: Review heat engine operation, efficiency calculations, and the laws of thermodynamics.  Fluid mechanics: Be prepared to solve problems involving fluid pressure, buoyancy, and fluid flow using Bernoulli’s principle and the continuity equation. Do not write outside the  Electrical engineering: Study circuit analysis for both AC and DC systems, focusing on power, efficiency, and the behavior of components like resistors, capacitors, and inductors.  Control systems: Understand how sensors, actuators, and feedback loops are used to control engineering systems. box IB/M/Jun24/7408/3BC 4 Do not write outside the IB/M/Jun24/7408/3BC Section B Answer all questions in this section. box 0 1 A heavy turntable is mounted on a fixed base. The turntable can rotate freely on a low-friction bearing. 0 1 . 1 Figure 1 shows a propeller unit fixed to the centre of the turntable. The propeller unit consists of a motor-driven propeller and a battery. The propeller and the turntable have a common axis of rotation. Figure 1 At first, the turntable and the propeller are at rest. The propeller motor is switched on and the propeller quickly reaches a high final angular speed. The propeller rotates clockwise when viewed from above. Compare, with reference to angular momentum, the motions of the turntable and the propeller. [3 marks] Question 1 continues on the next page Turn over ► 5 Do not write outside the box IB/M/Jun24/7408/3BC turntable. Figure 2 A small steel mass is held by an electromagnet above the top surface of the turntable. The diameter of the turntable is about half a metre. The turntable rotates freely at an initial angular speed ω1. The switch is opened so that the mass falls and sticks to the surface of the turntable. This changes the angular speed of the turntable to ω2. The steel mass can be considered to be a point mass. Describe how to determine the moment of inertia of the turntable using observations of ω1 and ω2. In your answer you should:  suggest how ω1 and ω2 are measured  state any other measurements needed and name the equipment used to make them  explain how the moment of inertia of the turntable is determined from the measurements. [6 marks] 0 1 . 2 Figure 2 shows an arrangement used to determine the moment of inertia of the 6 Do not write outside the box IB/M/Jun24/7408/3BC Turn over ► 9 7 Do not write outside the box There are no questions printed on this page IB/M/Jun24/7408/3BC DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED 8 Do not write outside the box IB/M/Jun24/7408/3BC 0 2 Figure 3 shows an excavator. Figure 3 The bucket position can be changed by moving the boom and arm and by rotating the platform about the vertical axis of rotation. For the purposes of this question, assume that the excavator tracks do not move. Question 2 continues on the next page Turn over ► 9 Do not write outside the box IB/M/Jun24/7408/3BC The bucket is moved to a new position by rotating the platform about the axis of rotation. Figure 4 shows the variation in angular velocity ω with time t for the rotation of the platform about the vertical axis. Figure 4 0 2 . 1 The total angular displacement of the platform is 2.52 rad during the movement of the bucket. Show that ωmax is about 0.9 rad s−1. [3 marks] 10 Do not write outside the box IB/M/Jun24/7408/3BC At the same time as the platform is rotating, the bucket is moved up and down, and away from and towards the cab. The moment of inertia of the rotating parts of the excavator about the axis of rotation is I. Figure 5 shows how I varies with t for the same time period as Figure 4. Figure 5 0 2 . 2 Torque must be applied to the platform to change its angular velocity and to overcome friction at the platform bearing. Show that the torque applied to the platform is at a maximum at time t = 2.1 s. [3 marks] Question 2 continues on the next page Turn over ► 11 Do not write outside the box IB/M/Jun24/7408/3BC 0 2 . 3 Deduce whether the maximum power applied to the platform occurs at the same time of 2.1 s. [2 marks] 8 12 Do not write outside the box Turn over for the next question IB/M/Jun24/7408/3BC DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED Turn over ► 13 Do not write outside the box IB/M/Jun24/7408/3BC 0 3 The Lenoir engine was the first successful internal combustion engine. Figure 6 shows the basic form of the Lenoir engine. The piston rod drives a crankshaft which is not shown. The fuel is a mixture of gas and air. Figure 6 Figure 7 shows an indicator diagram for the space L, taken during a test on a Lenoir engine. Figure 7 14 Do not write outside the box IB/M/Jun24/7408/3BC In one cycle the following changes occur in L.  Induction. The piston starts at the left-hand end of the cylinder. It moves to the right and fuel passes through the open inlet valve V1 into L. Figure 6 shows the piston during this induction process, with V1 open.  Ignition. When the piston is nearly halfway along the cylinder, V1 is closed. A spark ignites the fuel causing a sudden rise in pressure.  Expansion. The hot gases expand and the piston moves to the end of the stroke.  Exhaust. The exhaust valve V2 opens. The piston moves to the left. The exhaust gases are expelled at atmospheric pressure. The same processes are repeated in space R one half of a revolution of the crankshaft later than in L. So when the piston is moving to the left, induction, ignition and expansion occur in R at the same time as the exhaust process occurs in L. 0 3 . 1 The indicator diagram is for a rotational speed of the crankshaft of 120 rev min−1. Determine, using Figure 7, the indicated power of the engine. Assume that the indicator diagram for R is identical to the indicator diagram for L. [5 marks] indicated power = W Question 3 continues on the next page Turn over ► 15 Do not write outside the box IB/M/Jun24/7408/3BC 0 3 . 2 The following data are taken during the test on the engine: fuel consumption = 6.44 × 10−4 m3 s−1 calorific value of fuel = 18.0 × 106 J m−3 torque at crankshaft = 39.0 N m rotational speed = 120 rev min−1 Calculate the input power and the output (brake) power of the engine. [2 marks] input power = W output power = W 0 3 . 3 The output power of a four-stroke petrol engine of a similar working volume to that of the Lenoir engine is about 150 kW. Suggest two reasons for the very low output power of the Lenoir engine compared with a four-stroke petrol engine. [2 marks] 1 2 16 Do not write outside the box IB/M/Jun24/7408/3BC Turn over for the next question Turn over ► 0 3 . 4 Which statement is correct? Tick () one box. [1 mark] Thermal efficiency is a measure of how much of the indicated power is converted into output power. Overall efficiency is the product of mechanical efficiency and thermal efficiency. Mechanical efficiency is equal to friction power divided by indicated power. Input power is equal to indicated power plus friction power. 10 17 Do not write outside the box IB/M/Jun24/7408/3BC 0 4 . 1 The first law of thermodynamics can be expressed by the equation Q = ΔU + W. State the meaning of each term in this equation. [2 marks] Q ΔU W 0 4 . 2 A system consists of a perfectly insulated room containing only an empty refrigerator. The refrigerator is connected to the mains electricity and the refrigerator door is open. Deduce, by applying the first law of thermodynamics, whether the internal energy of the room increases, decreases or stays the same. [3 marks] 18 Do not write outside the box IB/M/Jun24/7408/3BC One definition of an ideal heat engine is: ‘a device which provides the maximum possible output of work from a given input of energy by heat transfer.’ Figure 8 shows a heat engine that appears to agree with this definition. The engine takes in energy from a high-temperature source and work is done by the engine. Figure 8 0 4 . 3 Complete Figure 8 so that the engine obeys the second law of thermodynamics. [1 mark] 0 4 . 4 Explain why the maximum theoretical efficiency of an ideal heat engine must be less than 100%. [2 marks] END OF QUESTIONS 8 19 Do not write outside the IB/M/Jun24/7408/3BC There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED box 20 Question number Additional page, if required. Write the question numbers in the left-hand margin. IB/M/Jun24/7408/3BC Do not write outside the box 21 Do not write outside the box IB/M/Jun24/7408/3BC Question number Additional page, if required. Write the question numbers in the left-hand margin. Copyright information For confidentiality purposes, all acknowledgements of third-party copyright material are published in a separate booklet. This booklet is published after each live examination series and is available for free download from Permission to reproduce all copyright material has been applied for. In some cases, efforts to contact copyright-holders may have been unsuccessful and AQA will be happy to rectify any omissions of acknowledgements. If you have any queries please contact the Copyright Team. Copyright © 2024 AQA and its licensors. All rights reserved. A-level PHYSICS 7408/3BC Paper 3 Section B Engineering physics Mark scheme June 2024 Version: 1.0 Final MARK SCHEME – A-LEVEL PHYSICS – 7408/3BC – JUNE 2024 Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation events which all associates participate in and is the scheme which was used by them in this examination. The standardisation process ensures that the mark scheme covers the students’ responses to questions and that every associate understands and applies it in the same correct way. As preparation for standardisation each associate analyses a number of students’ scripts. Alternative answers not already covered by the mark scheme are discussed and legislated for. If, after the standardisation process, associates encounter unusual answers which have not been raised they are required to refer these to the Lead Examiner. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of students’ reactions to a particular paper. Assumptions about future mark schemes on the basis of one year’s document should be avoided; whilst the guiding principles of assessment remain constant, details will change, depending on the content of a particular examination paper. No student should be disadvantaged on the basis of their gender identity and/or how they refer to the gender identity of others in their exam responses. A consistent use of ‘they/them’ as a singular and pronouns beyond ‘she/her’ or ‘he/him’ will be credited in exam responses in line with existing mark scheme criteria. Further copies of this mark scheme are available from Copyright information AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre. Copyright © 2024 AQA and its licensors. All rights reserved. 2 MARK SCHEME – A-LEVEL PHYSICS – 7408/3BC – JUNE 2024 Physics - Mark scheme instructions to examiners 1. General The mark scheme for each question shows:  the marks available for each part of the question  the total marks available for the question  the typical answer or answers which are expected  extra information to help the Examiner make his or her judgement and help to delineate what is acceptable or not worthy of credit or, in discursive answers, to give an overview of the area in which a mark or marks may be awarded. The extra information is aligned to the appropriate answer in the left-hand part of the mark scheme and should only be applied to that item in the mark scheme. At the beginning of a part of a question a reminder may be given, for example: where consequential marking needs to be considered in a calculation; or the answer may be on the diagram or at a different place on the script. In general the right-hand side of the mark scheme is there to provide those extra details which confuse the main part of the mark scheme yet may be helpful in ensuring that marking is straightforward and consistent. 2. Emboldening 2.1 In a list of acceptable answers where more than one mark is available ‘any two from’ is used, with the number of marks emboldened. Each of the following bullet points is a potential mark. 2.2 A bold and is used to indicate that both parts of the answer are required to award the mark. 2.3 Alternative answers acceptable for a mark are indicated by the use of or. Different terms in the mark scheme are shown by a / ; eg allow smooth / free movement. 3. Marking points 3.1 Marking of lists This applies to questions requiring a set number of responses, but for which candidates have provided extra responses. The general principle to be followed in such a situation is that ‘right + wrong = wrong’. Each error / contradiction negates each correct response. So, if the number of errors / contradictions equals or exceeds the number of marks available for the question, no marks can be awarded. However, responses considered to be neutral (often prefaced by ‘Ignore’ in the mark scheme) are not penalised. 3.2 Marking procedure for calculations