44 questions. Try each one, then open the answer to check yourself and read the explanation.
When a brick is taken from the earth's surface to the moon, its mass
Answer: A (remains constant.)
Mass is the amount of matter in a body and does not depend on where it is. Only its weight changes on the moon.
The resultant of two forces is 50N. If the forces are perpendicular to each other and one of them makes an angle of 30° with the resultant, find its magnitude.
Answer: C (43.3N.)
Two perpendicular forces are the components of the resultant. The one at 30° to the resultant is 50 cos 30° ≈ 43.3 N.
The pair of physical quantities that are scalar only are
Answer: A (volume and area.)
Volume and area have size only. Moment, momentum, displacement and impulse all have a direction, so they are vectors.
A simple pendulum of length 0.4m has a period of 2s. What is the period a similar pendulum of length 0.8m at the same place?
Answer: C (2√2s.)
T ∝ √L. Doubling the length multiplies the period by √2: T = 2√2 s.
A train with an initial velocity of 20ms−1 is subjected to a uniform deceleration of 2m−2. The time required to bring the train to a complete halt is
Answer: B (10s.)
t = (v − u)/a = (0 − 20) ÷ (−2) = 10 s.
Calculate the apparent weight loss of a man weighing 70kg in an elevator moving downwards with an acceleration of 1.5ms−2. [g = 10ms−2]
Answer: D (105N.)
Apparent weight = m(g − a) = 70 × 8.5 = 595 N, compared with a true weight of 700 N. The loss is ma = 70 × 1.5 = 105 N.
A piece of cork floats in a liquid. What fraction of its volume will be immersed in the liquid? [Density of the cork = 0.25 × 103kgm−3, density of the liquid = 1.25 × 103kgm−3]
Answer: C (0.2.)
For a floating body, fraction immersed = density of body ÷ density of liquid = 0.25 ÷ 1.25 = 0.2.
An object is moving with a velocity of 5ms−1. At what height must a similar body be situated to have a potential energy equal in value with kinetic energy of the moving body?
Answer: C (1.3m.)
mgh = ½mv2, so h = v2/2g = 25 ÷ 20 = 1.25 m ≈ 1.3 m (g = 10 m s−2).
If a pump is capable of lifting 5000 kg of water through a vertical height of 60 m in 15 min, the power of the pump is
Answer: C (3.3 × 103Js−1)
Power = mgh/t = 5000 × 10 × 60 ÷ (15 × 60) ≈ 3333 W = 3.3 × 103 J s−1.
The coefficient of friction between two perfectly smooth surface is
Answer: D (zero.)
Perfectly smooth surfaces give no friction at all, so the coefficient of friction is zero.
What effort will a machine of efficiency 90% apply to lift a load of 180N if its efforts arm is twice as long as its load arm?
Answer: C (100N.)
VR = effort arm ÷ load arm = 2. MA = 0.9 × 2 = 1.8. Effort = 180 ÷ 1.8 = 100 N.
Calculate the work done when a force of 20N stretches a spring by 50mm.
Answer: A (0.5J.)
Work done in stretching = ½Fe = ½ × 20 × 0.05 = 0.5 J.
At what depth below the sea-level would one experience a change of pressure equal to one atmosphere? [Density of sea water = 1013kgm−3 one atmosphere = 1.01 × 105Nm−2 g = 10ms−2]
Answer: C (10.0m.)
p = hρg, so h = p/(ρg) = 1.01 × 105 ÷ (1013 × 10) ≈ 10 m.
Calculate the length which corresponds to a temperature of 20°C if the ice and steam points of an ungraduated thermometer are 400 mm apart.
Answer: D (80mm.)
100°C corresponds to 400 mm, so 1°C is 4 mm and 20°C is 20 × 4 = 80 mm above the ice point.
A wire of length 100.0m at 30°C has linear expansivity of 2 × 10−5K−1. Calculate the length of the wire at a temperature of −10°C.
Answer: D (99.92m.)
Change in length = αLΔθ = 2 × 10−5 × 100 × (−40) = −0.08 m. New length = 100 − 0.08 = 99.92 m.
A gas at a pressure of 105Nm−2 expands from 0.6m3 to 1.2m3 at constant temperature, the work done is
Answer: D (6.0 × 104J.)
Taking the pressure as constant, work done = pΔV = 105 × (1.2 − 0.6) = 6.0 × 104 J.
Two liquids X and Y having the same mass are supplied with the same quantity of heat. If the temperature rise in X is twice that of Y, the ratio of specific heat capacity of X to that of Y is
Answer: B (1:2.)
Q = mcΔθ is the same for both, so c is inversely proportional to Δθ. X rises twice as much, so cX : cY = 1 : 2.
Foods cook quicker in salt water than in pure water because of the effect of
Answer: A (dissolved substances on the boiling point.)
Dissolved salt raises the boiling point of water, so salt water boils at a higher temperature and food cooks faster.
What will happen to the boiling point of pure water when it is heated in a place 30m below sea level?
Answer: A (It will be more than 100°C.)
Below sea level the atmospheric pressure is greater than normal, and a higher pressure raises the boiling point above 100°C.
The rise or fall of a liquid in a narrow tube is because of the
Answer: B (surface tension of the liquid.)
Capillary rise or fall is caused by surface tension together with the adhesion between the liquid and the tube.
The mechanism of heat transfer from one point to another through the vibration of the molecules of the medium is
Answer: B (conduction.)
In conduction the molecules vibrate about fixed positions and pass energy on to their neighbours, without the medium itself flowing.
A wave that travels through stretched strings is known as
Answer: C (mechanical wave.)
A wave on a string needs the material of the string to carry it, so it is a mechanical wave.
A transverse wave and a longitudinal wave travelling in the same direction in a medium differ essentially in their
Answer: C (direction of vibration of the particles of the medium.)
In a transverse wave the particles vibrate at right angles to the direction of travel; in a longitudinal wave they vibrate along it.
What is the velocity of sound at 100°C if the velocity of sound at 0°C is 340ms−1?
Answer: C (397m−1)
The speed of sound is proportional to the square root of the absolute temperature: v = 340 × √(373/273) ≈ 340 × 1.17 ≈ 397 m s−1.
If a sonometer has a fundamental frequency of 450Hz, what is the frequency of the fifth overtone?
Answer: A (2700Hz.)
A stretched string gives all harmonics; the fifth overtone is the sixth harmonic: 6 × 450 = 2700 Hz.
A man 1.5m tall is standing 3m in front of a pinhole camera whose distance between the hole and the screen is 0.1m. What is the height of the image of the man on the screen?
Answer: A (0.05m.)
Image height = object height × image distance ÷ object distance = 1.5 × 0.1 ÷ 3 = 0.05 m.
A ray of light passing through the centre of curvature of a concave mirror is reflected by the mirror at
Answer: A (0°.)
A ray through the centre of curvature travels along a radius, so it meets the mirror along the normal (angle of incidence 0°) and is reflected straight back at 0°.
From the diagram above, calculate the incident angle i.
Answer: D (61°.)
The refracted ray runs along the boundary, so i is the critical angle for glass to water: sin i = 1.33 ÷ 1.52 ≈ 0.875, giving i ≈ 61°.
Total internal reflection will not occur when light travels from
Answer: B (water into glass.)
Total internal reflection can only happen when light goes from a denser to a less dense medium. Water into glass is less dense to denser, so it cannot occur.
What does the diagram above represent?
Answer: B (microscope in normal use.)
The object sits just beyond the focal point Fo of the objective, which forms a real, magnified image inside the focus of the eyepiece. The eyepiece then gives a large virtual image I2: a compound microscope used normally.
If the linear magnification of the objective and eyepiece convex lenses of a compound microscope are 4 and 7 respectively, calculate the angular magnification of the microscope.
Answer: D (28.)
The total magnification of a compound microscope is the product of the two lens magnifications: 4 × 7 = 28.
The angle of deviation of light of various colours passing through a triangular prism increases in the order
Answer: A (red → green → blue.)
Red is deviated least and violet most, so the deviation increases from red to green to blue.
Calculate the force acting on an electron of charge 1.5 × 10−19C placed in an electric field of intensity 105Vm−1.
Answer: D (1.5 × 10−14N.)
F = qE = 1.5 × 10−19 × 105 = 1.5 × 10−14 N.
Capacitors are used in the induction coil to
Answer: C (prevent electric sparks.)
The capacitor across the make-and-break contacts absorbs the surge when the circuit breaks, preventing sparking and making the current fall faster.
A cell of emf 1.5V is connected in series with a 1Ω resistor and a current of 0.3A flows through the resistor. Find the internal resistance of the cell.
Answer: A (4.0Ω.)
E = I(R + r): 1.5 = 0.3(1 + r), so 1 + r = 5 and r = 4.0 Ω.
An electric device is rated 2000W, 250V. Calculate the maximum current it can take.
Answer: B (8A.)
I = P/V = 2000 ÷ 250 = 8 A.
When a charge moves through an electric circuit in the direction of an electric force, it
Answer: C (loses potential energy and gains kinetic energy.)
When a charge moves the way the electric force pushes it, the field does work on it: electrical potential energy is turned into kinetic energy.
To convert a galvanometer to a voltmeter, a
Answer: A (high resistance is connected to it in series.)
A voltmeter must draw very little current, so a large resistance (multiplier) is put in series with the galvanometer.
Induced emfs are best explained using
Answer: B (Faraday's law.)
Faraday's law says an e.m.f. is induced whenever the magnetic flux through a circuit changes, and its size equals the rate of change of flux. Lenz's law only adds the direction.
If a current of 2.5A flows through an electrolyte for 3 hours and 1.8g of a substance is deposited, what is the mass of the substance that will be deposited if a current of 4A flows through it for 4.8 hours?
Answer: C (4.6g.)
Mass ∝ It. m = 1.8 × (4 × 4.8) ÷ (2.5 × 3) = 1.8 × 19.2 ÷ 7.5 ≈ 4.6 g.
Calculate the energy of the third level of an atom if the ground state energy is −24.8eV
Answer: C (−2.75eV.)
En = E1/n2, so E3 = −24.8 ÷ 9 ≈ −2.75 eV.
In photo-emission, the number of photoelectrons ejected per second depends on the
Answer: D (intensity of the beam.)
Each photon can free one electron. A more intense beam carries more photons per second, so more photoelectrons are emitted per second.
The particle nature of light is demonstrated by the
Answer: A (photoelectric effect.)
The photoelectric effect can only be explained if light comes in packets (photons), which shows its particle nature. Diffraction is a wave effect.
The energy of a photon having a wavelength of 10−10m is (h = 6.63 × 10−34Js c = 3.0 × 108ms−1)
Answer: A (2.0 × 10−15J.)
E = hc/λ = 6.63 × 10−34 × 3.0 × 108 ÷ 10−10 ≈ 2.0 × 10−15 J.