30 reviewed questions with answers and explanations.
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In a hydrostatic model, the head-to-feet blood-pressure difference is 1.65 ×10⁴ Pa. Find the vertical height difference using density 1.1 ×10³ kg/m³ and g =10 m/s².
A: 1.5 m
For the stated hydrostatic model, ΔP =ρgh. Thus h =(1.65 ×10⁴)/(1.1 ×10³ ×10) =1.5 m.
AI-reviewed · calculation checkedIf the net force acting on a particle remains zero, its linear momentum will
A: Be constant
The net force equals the time rate of change of momentum: F_net =dp/dt. If the net force remains zero, momentum has zero rate of change and stays constant.
AI-reviewed · calculation checkedOn a wire’s elastic loading curve, force rises linearly from 0.10 N at extensionE =0.05 m to 0.20 N at extensionF =0.10 m. Find the additional energy stored fromE toF.
B: 7.5 ×10⁻³ J
Between extensions 0.05 m and 0.10 m, force rises linearly from 0.10 N to 0.20 N. The added elastic energy is the trapezium area:½(0.10 +0.20)(0.10 −0.05) =0.0075 J.
AI-reviewed · calculation checkedThe separation between two 10 kg point masses is tripled. What fraction of their original gravitational attraction remains?
A: One ninth
Gravitational attraction varies inversely with separation squared. Replacing r by 3 r gives F_new/F_old =r²/(3 r)² =1/9. The masses remain unchanged.
AI-reviewed · calculation checkedThe component of force along motion rises linearly from zero at displacement 0 toF newtons at displacementx metres. Find the work done over that interval.
C: Fx/2 J
Work is the area under the force-distance graph. A force rising linearly from zero toF over distancex forms a triangle, so W =½ ×x ×F =Fx/2.
AI-reviewed · calculation checkedTwo forces act on a body:10 N north and 10 N east. Find the resultant magnitude and its direction measured from north.
C: 10√2 N,45° east of north
North and east components are perpendicular and both 10 N. The magnitude is√(10² +10²) =10√2 N, and equal components give 45° east of north.
AI-reviewed · calculation checkedWhich eye defect is commonly corrected by adding cylindrical power to a spectacle lens?
D: Astigmatism
Regular astigmatism gives different focusing powers in different directions across the eye. A cylindrical lens supplies direction-dependent power to compensate for that difference.
AI-reviewed · source checkedWhich listed quantity is transported from place to place by a travelling wave?
D: Energy
A travelling wave transfers energy from one region to another. Amplitude, wavelength and frequency describe the wave, while energy is what the propagating disturbance transports.
AI-reviewed · source checkedA 0.6 m stretched string fixed at both ends has fundamental frequency 220 Hz. Find the transverse-wave speed.
A: 264 ms-1
The fundamental mode of a string fixed at both ends has half a wavelength along its length. Thus λ =2 L =1.2 m and v =fλ =220 ×1.2 =264 m/s.
AI-reviewed · calculation checkedHeat is carried away from a motor-car radiator’s fins by air flowing over them mainly through
D: Convection
Air flowing over radiator fins carries heat away by forced convection. Heat first reaches the fin surfaces through the metal, but its transfer from the surface into moving air is convective.
AI-reviewed · source checkedAt fixed liquid temperature, blowing relatively dry air across its surface aids evaporation mainly by
A: Reducing vapour partial pressure in the air just above the liquid
Moving relatively dry air sweeps vapour away from just above the liquid. This lowers the local vapour partial pressure and reduces condensation back onto the liquid, increasing net evaporation.
AI-reviewed · source checkedFind the pressure of 3 mol of ideal gas at 27°C in volume 10⁻³ m³. Use R =8.3 J/(mol·K) and 27°C ≈300 K.
C: 7.47 ×10⁶ Pa
Using 27°C ≈300 K, the ideal-gas law gives P =nRT/V =(3 ×8.3 ×300)/10⁻³ =7.47 ×10⁶ Pa. Temperature must be in kelvin.
AI-reviewed · calculation checkedTo produce an enlarged and erect image with a concave mirror, the object must be positioned
A: Between the principal focus and the pole
With an object inside the focal length of a concave mirror, reflected rays diverge and their backward extensions form an upright virtual image. Its magnification is greater than one.
AI-reviewed · source checkedThe colours seen in soap bubbles are due to
C: Interference
Light reflected from the front and back surfaces of the thin soap film takes different optical paths. Their interference reinforces some wavelengths and suppresses others, producing colours that vary with film thickness.
AI-reviewed · source checkedThe fading persistence of sound in a room through many overlapping reflections after the source stops is called
A: Reverberation
Reverberation is the fading persistence of sound caused by many overlapping reflections after the source stops. A distinct delayed repetition is called an echo.
AI-reviewed · source checkedUnder Newton’s law of cooling with a constant heat-transfer coefficient, the heat-loss rate of a warmer body is proportional to
B: Difference in temperature between the body and its surrounding
Newton’s law of cooling models heat-loss rate as H =k(T_body −T_surroundings) when the heat-transfer coefficient is effectively constant. It is the temperature difference that drives the heat flow.
AI-reviewed · calculation checkedAn electric iron’s resistive element is rated 1000 W at 230 V. Find its resistance at the rated operating condition.
D: 52.9 Ohms
For a resistive element, P =V²/R. Therefore R =230²/1000 =52.9 Ω at its rated operating condition.
AI-reviewed · calculation checkedAn electric-field sketch shows arrows pointing away from each of two point chargesX andY. What are their signs?
A: Both X and Y are positive
Electric field lines point away from positive charges and toward negative charges. Since the arrows emerge from bothX andY, both charges are positive.
AI-reviewed · source checkedWhich part of the eye changes the pupil’s size to control the amount of light reaching the retina?
A: Iris
Muscles in the iris change the pupil’s diameter, controlling how much light enters the eye and reaches the retina. The iris therefore acts as the adjustable aperture.
AI-reviewed · source checkedA 10 μF capacitor carries charge 100 μC. Find its stored energy.
A: 5 ×10⁻⁴ J
Capacitor energy is U =Q²/(2 C). With Q =100 ×10⁻⁶ C and C =10 ×10⁻⁶ F, U =(10⁻⁴)²/(2 ×10⁻⁵) =5 ×10⁻⁴ J.
AI-reviewed · calculation checkedAcross 12 V, a circuit draws 2 A through a 2 Ω resistor, a parallel pair of 3 Ω andX, and a 1.5 Ω resistor, in that series order. FindX.
A: 15 Ω
Total resistance is 12/2 =6 Ω. The parallel pair therefore has 6 −2 −1.5 =2.5 Ω. Solving 1/2.5 =1/3 +1/X gives 1/X =1/15, so X =15 Ω.
AI-reviewed · calculation checkedWhich particle normally triggers the fission chain reaction in a nuclear fission reactor?
B: Neutron
A neutron absorbed by a suitable fissile nucleus can trigger fission. The resulting fission releases more neutrons, which can sustain the chain reaction in a reactor.
AI-reviewed · source checkedAt what frequency does a 2.5 μF capacitor have reactance 250 Ω?
D: 800/π Hz
Capacitive reactance is X_C =1/(2πfC). Thus f =1/(2π ×250 ×2.5 ×10⁻⁶) =800/π Hz.
AI-reviewed · calculation checkedWhat percentage of the original undecayed nuclei remains after five half-lives, rounded to the nearest whole percent?
B: 3 %
After five half-lives, the fraction of original undecayed nuclei is(1/2)⁵ =1/32. As a percentage this is 3.125%, which rounds to 3% to the nearest whole percent.
AI-reviewed · calculation checkedIn the nuclear reaction ²³₁₁Na +X → ²⁰₉F +⁴₂He, identify particleX.
A: Neutron
Conservation of nucleon number gives 23 +A_X =20 +4, so A_X =1. Conservation of charge gives 11 +Z_X =9 +2, so Z_X =0. A particle with mass number 1 and charge number 0 is a neutron.
AI-reviewed · calculation checkedWhich feature helps make a moving-coil galvanometer sensitive to small currents?
B: A strong permanent magnet producing a strong field
A stronger magnetic field gives a larger turning effect on the current-carrying coil. This improves current sensitivity when coil turns, area and spring stiffness are unchanged.
AI-reviewed · source checkedPure silicon can be converted to a p-type material by adding a controlled amount of
B: Trivalent atoms
Trivalent dopants have one fewer valence electron than silicon. They introduce acceptor states and holes, making holes the majority carriers in p-type silicon.
AI-reviewed · source checkedFor a fixed power transmitted through a line, using a higher voltage mainly reduces
A: Resistive heating in the transmission conductors
For the same transmitted power, increasing voltage reduces current because I =P/V. Resistive heating in the transmission conductors is I²R, so reducing current sharply reduces this loss.
AI-reviewed · calculation checkedFind the energy of a photon of frequency 3.0 ×10⁵ Hz to two significant figures. Use h =6.63 ×10⁻³⁴ J·s.
B: 2.0 ×10⁻²⁸ J
Photon energy is E =hf =(6.63 ×10⁻³⁴)(3.0 ×10⁵) =1.989 ×10⁻²⁸ J. To two significant figures this is 2.0 ×10⁻²⁸ J.
AI-reviewed · calculation checkedThe carbon-granule microphone works on the principle of change in
D: Resistance
Sound pressure changes the contact between carbon granules, varying their electrical resistance. With an applied bias, this resistance change produces a corresponding electrical signal.
AI-reviewed · source checked