25 reviewed questions with answers and explanations.
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Which of the following is a fundamental unit?
D: Second
The second is the SI base unit of time. Newton, watt and joule are derived units built from kilogram, metre and second.
AI-reviewed · source checkedAn engine supplies useful mechanical power P to keep a vehicle moving at constant speed v. What driving force does it provide?
A: P/v
Mechanical power for a force along the direction of motion is P = Fv. Dividing by speed gives the engine’s driving force F = P/v.
AI-reviewed · calculation checkedWhat liquid-column height supports atmospheric pressure 102000 N/m² if liquid density is 2600 kg/m³ and g = 10 m/s²? Give the answer to two decimal places.
C: 3.92m
Hydrostatic pressure is p = ρgh. Thus h = 102000/(2600 × 10) = 3.923… m, or 3.92 m to two decimal places.
AI-reviewed · calculation checkedA platinum wire has resistance 0.75 Ω at 0 °C and 1.05 Ω at 100 °C. Assuming linear variation, find its temperature when resistance is 0.90 Ω.
B: 50.0 °C
The 0–100 °C resistance change is 1.05 − 0.75 = 0.30 Ω. The measured rise is 0.90 − 0.75 = 0.15 Ω, half the interval. Temperature is therefore 50.0 °C.
AI-reviewed · calculation checkedA fixed amount of gas is cooled at constant volume without condensation. Its pressure decreases because its molecules
A: Collide less frequently with the walls of the container.
Cooling lowers the molecules’ average kinetic energy and speed. At fixed volume they strike the walls less often and with less momentum change per collision, reducing the gas pressure.
AI-reviewed · source checkedA 1 kg copper block at 100 °C is placed on ice at 0 °C. Neglect heat loss. Find the mass melted to the nearest gram, using copper’s specific heat capacity 400 J/(kg·K) and ice’s latent heat of fusion 333 × 10³ J/kg.
C: 120g
The copper loses Q = mcΔT = 1 × 400 × 100 = 40000 J. This melts ice of mass Q/L = 40000/333000 = 0.12012… kg, or 120 g to the nearest gram.
AI-reviewed · calculation checkedAt external pressure 750 mmHg, what change is needed to make pure water boil at 100 °C?
A: Increase the external pressure
Pure water boils near 100 °C at about 760 mmHg. At 750 mmHg it boils slightly below 100 °C. Raising the external pressure to about 760 mmHg raises the boiling point to 100 °C.
AI-reviewed · source checkedIn ordinary heat-transfer experiments, which statements are correct? I. Land and sea breezes are natural convection currents. II. Convection occurs in liquids or gases, rather than solids retaining their fixed shape. III. The vacuum gap in a thermos flask prevents heat transfer by convection only.
A: I and II only
Land and sea breezes arise from natural convection. In ordinary heat-transfer experiments, convection is bulk motion of a liquid or gas. A vacuum suppresses both conduction and convection across the gap, so III is false.
AI-reviewed · source checkedGeometrical shadows and eclipses result primarily from the
B: Rectilinear propagation of light
In a uniform medium, light travels approximately in straight lines. An opaque object blocks those paths and produces a shadow; an eclipse occurs when a celestial body blocks the light reaching another body or observer.
AI-reviewed · source checkedAn object 3 cm high is placed vertically 10 cm in front of a concave mirror. Its image is 40 cm from the mirror. Find the magnitude of the image height.
D: 12.00 cm
The magnitude of magnification is image distance divided by object distance: 40/10 = 4. Therefore the image height has magnitude 4 × 3 = 12 cm.
AI-reviewed · calculation checkedWhat must be the distance between an object and a converging lens of focal length 20cm to produce an erect image two times the object height?
C: 10cm
An erect image from a converging lens is virtual: v = −2u. Substituting in 1/f = 1/u + 1/v gives 1/20 = 1/(2u). Hence u = 10 cm, inside the focal length.
AI-reviewed · calculation checkedIn an uncorrected short-sighted eye, light rays from a point on a very distant object are focused
A: In front of the retina
In an uncorrected short-sighted eye, parallel rays from a distant object converge before reaching the retina. A diverging corrective lens reduces the eye system’s convergence so the focus moves back onto the retina.
AI-reviewed · source checkedUnder white illumination, which primary colour does an ideal magenta surface absorb?
B: Green only
An ideal magenta surface reflects red and blue light and absorbs green. Under white illumination, the reflected red and blue combine to appear magenta.
AI-reviewed · source checkedIn a resonance tube closed at one end, the first resonant air-column length is 20 cm for a 480 Hz tuning fork. Neglect end correction and find the speed of sound.
D: 384 m/s
At the first resonance of a tube closed at one end, L = λ/4. Thus λ = 4 × 0.20 = 0.80 m and v = fλ = 480 × 0.80 = 384 m/s.
AI-reviewed · calculation checkedAn organ pipe closed at one end is 80 cm long. Neglect end correction. Find its fundamental frequency to the nearest hertz if sound speed is 340 m/s.
A: 106 Hz
For the fundamental of a pipe closed at one end, λ = 4L = 3.20 m. Frequency is 340/3.20 = 106.25 Hz, or 106 Hz to the nearest hertz.
AI-reviewed · calculation checkedAn insulated body is at rest in electrostatic equilibrium with positive net charge. Which statements are true? I. Positive charge exceeds negative charge. II. It creates an electric field. III. It stores electrostatic energy relative to its discharged state. IV. It carries a steady electric current.
C: I, II and III only
Positive net charge means there is more positive than negative charge, usually through an electron deficit. The charged body creates a field and stores electrostatic energy. At rest in electrostatic equilibrium, it carries no steady current.
AI-reviewed · source checkedWhich of the following is a vector?
B: Electric field
Electric field is force per unit positive test charge, so it has both magnitude and direction. Electric charge, potential difference and capacitance are scalars.
AI-reviewed · source checkedThree identical cells, each of emf 1.5 V and internal resistance 1.0 Ω, are connected in parallel with matching polarity across a 2.67 Ω load. Find the load current to two decimal places.
C: 0.50A
Identical cells in parallel retain emf 1.5 V and have internal resistance 1/3 Ω. The load current is 1.5/(2.67 + 1/3) = 0.4994… A, or 0.50 A to two decimal places.
AI-reviewed · calculation checkedIn a uniform metre bridge, a 2.0 Ω standard resistor occupies the gap beside the 0 cm end. The balance point is 55.0 cm from that end. Find the resistance in the other gap to two decimal places.
B: 1.64 Ohms
For a uniform metre bridge, resistance ratio equals wire-length ratio at balance. With 2.0 Ω beside the 0 cm end, 2.0/R = 55/45. Thus R = 2.0 × 45/55 = 1.64 Ω to two decimal places.
AI-reviewed · calculation checkedThe energy supplied by an electrical source per unit positive charge for a complete circuit is its
C: Electromotive force
Emf is the energy supplied by a source per unit charge passing through it. That energy is transferred around the complete circuit, including the source’s internal resistance. Its unit is the volt, or joule per coulomb.
AI-reviewed · source checkedWhich of the following is an essential physical property of the wires used for making fuses?
D: Low melting point.
A fuse element must melt when excessive current heats it sufficiently. Melting opens the circuit and stops the sustained overcurrent. A suitably low melting point supports this protective action.
AI-reviewed · source checkedFor the same transmitted power, using a higher voltage reduces energy lost in the transmission wires through
A: Heat dissipation
For the same transmitted power, increasing voltage reduces current because P = VI. Heating loss in the wires is I²R, so lowering current reduces heat dissipation.
AI-reviewed · source checkedA galvanometer with full-scale current 10 mA and coil resistance 30 Ω is converted to a 10 A ammeter. Which approximate resistor and connection are required?
B: 0.03 ohms shunt resistor
The full-scale coil voltage is 0.010 × 30 = 0.30 V. The shunt carries 10 − 0.010 = 9.99 A, so its resistance is 0.30/9.99 ≈ 0.03 Ω. It must be parallel to the coil.
AI-reviewed · calculation checkedWhat precaution should a manufacturer take to ensure that energy loss in a transformer is minimized?
B: Make the magnetic core from thin, electrically insulated metal sheets
A transformer core made from thin, electrically insulated metal laminations restricts large circulating eddy currents. This reduces unwanted heating in the core.
AI-reviewed · source checkedA photoemissive photocell works on the principle of
B: Emission of electrons by incident radiation
A photoemissive cell uses incident photons to release electrons from a photosensitive surface. Those electrons can be collected to produce a measurable current.
AI-reviewed · source checked