Master 2–3 mark short-answer conceptual questions from 2024 & 2025 Annual Examination Paper II, Model Paper II, and the 2025 syllabus, complete with Checking Hints rubrics, model solutions, and authentic E-Marking candidate scripts.
2025 Syllabus Outcome (11.3.1): identify transverse and longitudinal waves in mechanical media;
Differentiate between transverse waves and longitudinal waves with two examples of each.
✓ MODEL SOLUTION (Full Marks Guidance)
In transverse waves, particles vibrate perpendicular to wave propagation (e.g., water waves, light waves). In longitudinal waves, particles vibrate parallel to wave propagation creating compressions and rarefactions (e.g., sound waves in air, slinky compression waves).
2025 Syllabus Outcome (12.2.3): define the intensity of sound and state its SI unit;
Distinguish between loudness, pitch, and quality (timbre) of sound and state the physical wave factor on which each depends.
✓ MODEL SOLUTION (Full Marks Guidance)
Loudness depends on amplitude and surface area of the vibrating body; pitch depends on frequency; quality (timbre) depends on the waveform (harmonics/overtones).
If an object is placed at a distance of 2 cm from a convex mirror of focal length of 4 cm, then find the position of the image formed.
📋 Official Checking Hints (Marking Rubric • 3 Marks)
1 mark for the correct mirror formula: 1/f = 1/p + 1/q.
1 mark for the correct substitution with sign convention (for a convex mirror, f = -4 cm and p = +2 cm; or using standard positive focal length magnitude showing virtual image behind mirror).
1 mark for the correct calculated image position with unit (q = -4/3 cm = -1.33 cm using f = -4 cm, or q = -4 cm as shown in E-Marking exemplar, indicating a virtual image behind the convex mirror).
✓ MODEL SOLUTION (Full Marks Guidance)
Given Data:
•Object distance (p) = +2 cm
•Focal length of convex mirror (f) = −4 cm (virtual focus behind the mirror; note: in the AKU-EB E-Marking exemplar, f=4 cm is substituted into f1=p1+q1)
Formula:
f1=p1+q1⟹q1=f1−p1
Calculation (AKU-EB E-Marking Exemplar Method):
q1=41−21=41−2=−41
q=−4 cm
*(Note: Using strict Cartesian sign convention f=−4 cm gives q1=−41−21=−43⟹q=−1.33 cm. In both conventions, the negative sign of q indicates that a virtual, upright image is formed behind the convex mirror.)*
Examiner Commentary (Better Responses): Better responses correctly applied the mirror formula (1/f = 1/p + 1/q) to solve for the image position, providing step-by-step calculations and arriving at q = -4 cm (or -1.33 cm with negative focal length), indicating a virtual image formed behind the convex mirror with proper units.
⚠ WEAKER RESPONSE (Common Misconceptions & Lost Marks)
Weaker responses attempted to calculate image position using irrelevant formulas such as the simple pendulum formula, Newton's second law, wave speed v = fλ (multiplying 4 × 2 = 8 cm), Snell's law, or transformer formulas, or omitted units and sign conventions.
Examiner Suggestion for Improvement: Teachers are encouraged to use the images containing correct and incorrect solutions to conduct live problem-solving sessions. Highlight step-by-step calculations and common pitfalls (e.g., sign conventions for spherical mirrors) to reinforce conceptual clarity.
2025 Syllabus Outcome (13.4.5): describe the use of total internal reflection in:
a. optical fibre,
b. periscope;
Describe, how are light signals transmitted through an optical fibre.
📋 Official Checking Hints (Marking Rubric • 2 Marks)
1 mark for an incomplete description (identifying core/cladding structure or stating that light enters at an angle greater than the critical angle).
2 marks for a complete description: explaining that an optical fibre has a higher-refractive-index inner core surrounded by a lower-refractive-index cladding, and light signals striking the core-cladding boundary at an angle of incidence greater than the critical angle undergo continuous Total Internal Reflection (TIR) to travel through the fibre.
✓ MODEL SOLUTION (Full Marks Guidance)
An optical fibre consists of a thin, high-refractive-index glass or plastic inner core surrounded by a lower-refractive-index outer cladding.
When a modulated light signal enters one end of the optical fibre, it strikes the boundary between the inner core and outer cladding at an angle of incidence greater than the critical angle (θi>θc). As a result, the light ray undergoes repeated Total Internal Reflection (TIR) back and forth inside the core until it emerges at the receiving end with minimal energy loss.
Examiner Commentary (Better Responses): Better responses identified the key components of an optical fibre (inner core and outer cladding) and explained that light signals strike the core-cladding boundary at an angle greater than the critical angle, undergoing total internal reflection along the fibre.
⚠ WEAKER RESPONSE (Common Misconceptions & Lost Marks)
Weaker responses confused optical transmission with electrical current flow or radioactivity (e.g., claiming light signals are transmitted through an optical fibre by 'radioactive elements and flow of current' or 'deflecting electrons').
Examiner Suggestion for Improvement: Teachers are encouraged to use a laser pointer and acrylic rod to physically demonstrate total internal reflection, emphasising (1) refractive index differences between core and cladding, (2) the critical angle, and (3) avoiding conflation with electrical conduction.
2025 Syllabus Outcome (14.1.4): describe production and detection of electric charge;
Explain how a gold-leaf electroscope is used to detect the presence and nature (sign) of an unknown electric charge.
✓ MODEL SOLUTION (Full Marks Guidance)
Bringing a charged body near the brass disc causes the gold leaves to diverge. If the electroscope is first charged with a known sign, an increase in divergence indicates the same sign of charge, whereas a decrease indicates the opposite sign or an uncharged conductor.
2025 Syllabus Outcome (15.4.3): compare potential difference and electromotive force;
Differentiate between electromotive force (e.m.f.) and potential difference across a conductor.
✓ MODEL SOLUTION (Full Marks Guidance)
e.m.f. is the total energy supplied by a source per unit coulomb of charge around the complete circuit (measured across open terminals), whereas potential difference is the electrical energy converted into other forms per unit charge between two points in the external circuit.
2025 Syllabus Outcome (16.1.2): derive the effective/ equivalent resistance of resistors connected in series and in parallel;
Why are domestic electrical appliances connected in parallel rather than in series across the live and neutral mains wires?
✓ MODEL SOLUTION (Full Marks Guidance)
1.Every appliance receives the full standard mains voltage (220–240 V). 2. Each appliance can be switched on or off independently without breaking the circuit for other appliances.
2025 Syllabus Outcome (17.3.1): describe the pattern and direction of the magnetic field due to currents in straight wires and in solenoids;
i.Describe a condition under which a single electron can generate a magnetic field. (2 Marks)
ii.Will it be a weak or strong magnetic field? (1 Mark)
📋 Official Checking Hints (Marking Rubric • 3 Marks)
i. 2 marks (1 mark for each key point) for stating that the single electron must be in motion / moving through a conductor (creating an electric current) to generate a magnetic field around it.
ii. 1 mark for stating that the magnetic field generated by a single moving electron will be weak.
✓ MODEL SOLUTION (Full Marks Guidance)
(i) Condition for a single electron to generate a magnetic field (2 Marks):
A stationary electric charge produces only an electric field, whereas a moving electric charge constitutes an electric current and produces a magnetic field around its path. Therefore, when a single electron is in motion (or flowing through a conductor/circuit), it generates a magnetic field around it.
(ii) Strength of the magnetic field (1 Mark):
The magnetic field generated by a single moving electron will be extremely weak.
Examiner Commentary (Better Responses): Better responses focused on the motion of the electron or the flow of current, stating clearly that 'when an electron moves/flows in a circuit or conductor, it produces current that generates a magnetic field around it', and correctly identified the resulting field as weak.
⚠ WEAKER RESPONSE (Common Misconceptions & Lost Marks)
Weaker responses confused electrostatic attraction with magnetic field generation (claiming a single electron contacts a positive charge to create a 'strong magnetic field'), or invoked mutual induction or thermionic emission without mentioning electron motion.
Examiner Suggestion for Improvement: Teachers should emphasise that (1) only moving charges create magnetic fields, (2) single electrons produce exceptionally weak fields, and (3) terms like 'mutual induction' or 'charge attraction' are irrelevant to this context.
2025 Syllabus Outcome (17.4.3): describe the effect on the magnetic force of reversing the direction of current and magnetic field;
State Fleming's left-hand rule for the force on a current-carrying conductor in a magnetic field.
✓ MODEL SOLUTION (Full Marks Guidance)
Hold the thumb, forefinger, and middle finger of the left hand mutually perpendicular: if the Forefinger points in the direction of the Magnetic Field and the Middle finger in the direction of Conventional Current, the Thumb points in the direction of the Magnetic Force (Motion).
a. Name and define the principle on which a transformer works. b. Write ONE practical use of a transformer.
✓ MODEL SOLUTION (Full Marks Guidance)
a. Mutual induction: The phenomenon in which a changing electric current in a primary coil induces an electromotive force (e.m.f.) in a neighbouring secondary coil. b. Stepping up voltage at power stations for low-loss grid transmission or stepping down voltage for household appliances.
2025 Syllabus Outcome (19.5.7): describe the uses of logic gates.
State any TWO uses of logic gates in daily life.
📋 Official Checking Hints (Marking Rubric • 2 Marks)
1 mark for the first valid daily-life application of logic gates (e.g., burglar/security alarms, automatic street lights, safety thermostats).
1 mark for the second valid daily-life application of logic gates (e.g., microprocessors in computers/calculators, traffic light controllers, automatic doors).
✓ MODEL SOLUTION (Full Marks Guidance)
Uses of Logic Gates in Daily Life (Any TWO):
1.Home Security & Burglar Alarms: Logic gates (such as AND and OR gates) are used in burglar alarms and fire/smoke alarm circuits to trigger a siren when a door sensor or motion detector is activated while the alarm switch is armed.
2.Computers, Calculators & Digital Appliances: Logic gates form the fundamental building blocks of microprocessors and arithmetic logic units (ALUs) in computers, digital calculators, automatic washing machines, and traffic light controllers.
Examiner Commentary (Better Responses): Better responses provided clear, concrete examples of logic gate applications in daily life, such as their use in computers/calculators for arithmetic operations and in burglar/security alarm systems and kitchen appliances.
⚠ WEAKER RESPONSE (Common Misconceptions & Lost Marks)
Weaker responses merely listed logic gate types (NOR, NAND, OR, NOT) without stating any real-world applications, or gave vague statements like 'understanding computer language'.
Examiner Suggestion for Improvement: Teachers should emphasise that logic gates are building blocks of digital circuits and provide specific everyday examples like burglar alarms, traffic light controllers, calculators, and automatic doors, distinguishing gate names from their practical uses.
2025 Syllabus Outcome (19.2.2): describe the simple construction and use of an electron gun as a source of electron beam;
The picture that appears on the screen of a television, that uses cathode rays tube, becomes distorted when a powerful magnet is brought near the screen. Explain the given phenomena.
📋 Official Checking Hints (Marking Rubric • 2 Marks)
Explanation of cathode rays as moving charged particles (electrons)
Explanation of magnetic force (Lorentz force) deflecting the electron beam
✓ MODEL SOLUTION (Full Marks Guidance)
Cathode rays are beams of fast-moving electrons. When a powerful magnet is brought near the screen, the magnetic field exerts a magnetic force (Lorentz force) on these moving electrons, deflecting them from their original path and causing the picture on the screen to distort.
2025 Syllabus Outcome (19.2.2): describe the simple construction and use of an electron gun as a source of electron beam;
The picture on a cathode-ray tube (CRT) television screen becomes distorted when a powerful magnet is brought near it. Explain why.
✓ MODEL SOLUTION (Full Marks Guidance)
Cathode rays are beams of fast-moving negatively charged electrons. Bringing a strong magnet near the tube exerts a magnetic Lorentz force on the moving electrons, deflecting them away from their intended target pixels on the fluorescent screen.
2025 Syllabus Outcome (20.6.2): calculate the half-life of radioactive elements;
Suppose a radioactive element has an initial number of atoms (X) kept in a nuclear power station.
Calculate the number of radioactive atoms left after 10 half-lives.
📋 Official Checking Hints (Marking Rubric • 3 Marks)
1 mark for writing the correct half-life decay formula: N = N₀ × (1/2)^n (or N = N₀ / 2^t).
1 mark for substituting the correct values: N₀ = X and n = 10 -> N = X × (1/2)^10.
1 mark for writing the correct final answer: N = X / 1024 (or (1/1024)X atoms remaining).
✓ MODEL SOLUTION (Full Marks Guidance)
Given Data:
•Initial number of radioactive atoms (N0) = X
•Number of half-lives elapsed (n) = 10
Formula:
N=N0×(21)n
Substitution & Calculation:
N=X×(21)10=X×2101=1024X
Answer:
After 10 half-lives, 1024X (or 10241th of the original number of atoms X) will remain undecayed.
Examiner Commentary (Better Responses): Better responses systematically applied the formula N = N₀ × (1/2)^10 = X / 1024, or showed the step-by-step halving chain (X -> X/2 -> X/4 -> X/8 -> ... -> X/1024) across 10 half-lives.
⚠ WEAKER RESPONSE (Common Misconceptions & Lost Marks)
Weaker responses treated radioactive decay as linear subtraction or division (e.g., writing 10 - 1/2 = 9.5 radioactive atoms left, or 10 / 2 = 5 atoms, or N = N₀ × 12t).
Examiner Suggestion for Improvement: Teachers should emphasise the exponential nature of radioactive decay N = N₀(1/2)^n and use progressive halving diagrams (1 -> 2 -> 3 ... -> 10 half-lives) to contrast exponential reduction with linear subtraction.
2025 Syllabus Outcome (20.7.3): state the nature of the Sun consisting mostly of hydrogen and helium and radiates most of its energy;
A nuclear fusion reaction is very difficult to achieve as compared to the nuclear fission reaction. Justify the given statement in any THREE points.
📋 Official Checking Hints (Marking Rubric • 3 Marks)
First valid scientific point regarding repulsion/activation energy
Second valid scientific point regarding high temperature/pressure requirement
Third valid scientific point regarding containment challenges (plasma)
✓ MODEL SOLUTION (Full Marks Guidance)
1.Positively charged nuclei repel each other strongly due to electrostatic forces, requiring huge amounts of energy to bring them close enough for fusion.
2.Extremely high temperatures (millions of degrees Celsius) are required to give nuclei enough kinetic energy to overcome this electrostatic repulsion.
3.Containing such extremely hot plasma in a controlled environment is technologically very difficult compared to initiating a neutron-induced fission reaction.
2025 Syllabus Outcome (20.7.3): state the nature of the Sun consisting mostly of hydrogen and helium and radiates most of its energy;
A nuclear fusion reaction is much more difficult to achieve than a nuclear fission reaction. Justify this statement in THREE points.
✓ MODEL SOLUTION (Full Marks Guidance)
1.Positively charged light nuclei experience strong electrostatic repulsion as they approach each other. 2. Overcoming this Coulomb barrier requires extremely high kinetic energy corresponding to temperatures of millions of kelvins. 3. Containing such high-temperature plasma without melting solid reactor walls is technologically challenging.