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DU Ka Unit (Science Unit) practice questions

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Question 1Physics

Which SI unit is used to express the amount of electric current flowing through a conductor?

  1. Volt
  2. Ohm
  3. Ampere Correct answer.
  4. Coulomb

Explanation

Electric current is a base quantity in the SI system, and its unit is the ampere, defined by the force between parallel current-carrying conductors. The volt measures potential difference, the coulomb measures charge, and the ohm measures resistance, so none of those describe current itself.

Question 2Physics

A car travels 150 metres in 10 seconds at a steady speed. What is its speed?

  1. 1.5 m/s
  2. 150 m/s
  3. 0.067 m/s
  4. 15 m/s Correct answer.

Explanation

Speed is distance divided by time, so 150 metres divided by 10 seconds gives 15 metres per second. The other values come from multiplying, dividing in the wrong order, or misplacing the decimal point.

Question 3Physics

On the Moon the gravitational field strength is about one sixth of that on Earth. Compared with Earth, an astronaut on the Moon has:

  1. the same mass but a smaller weight Correct answer.
  2. the same mass and the same weight
  3. a smaller mass and a smaller weight
  4. a smaller mass but the same weight

Explanation

Mass measures the quantity of matter and does not change with location, so the astronaut's mass is unchanged. Weight is the gravitational force on that mass, given by mass times field strength, so a weaker field means a smaller weight.

Question 4Physics

Which statement correctly describes the energy transfer in an electric motor?

  1. Kinetic energy is converted mainly into electrical energy
  2. Chemical energy is converted mainly into electrical energy
  3. Electrical energy is converted mainly into kinetic energy Correct answer.
  4. Electrical energy is converted mainly into sound energy

Explanation

A motor uses the magnetic force on a current-carrying coil to produce rotation, so electrical energy supplied becomes mechanical kinetic energy, with some heating losses. The reverse conversion describes a generator, and the other options describe unrelated devices.

Question 5Physics

A ray of light strikes a plane mirror at an angle of incidence of 35 degrees. What is the angle between the incident ray and the reflected ray?

  1. 110 degrees
  2. 70 degrees Correct answer.
  3. 35 degrees
  4. 55 degrees

Explanation

The law of reflection states that the angle of reflection equals the angle of incidence, so the reflected ray also makes 35 degrees with the normal. The total angle between the two rays is therefore 35 plus 35, which equals 70 degrees.

Question 6Physics

Which of the following is a vector quantity?

  1. Mass
  2. Displacement Correct answer.
  3. Time
  4. Temperature

Explanation

A vector has both magnitude and direction, and displacement specifies how far and in which direction an object has moved. Temperature, mass, and time are scalars because they are fully described by magnitude alone.

Question 7Physics

Two identical resistors of 6 ohms each are connected in parallel. What is the total resistance of the combination?

  1. 1.5 ohms
  2. 3 ohms Correct answer.
  3. 6 ohms
  4. 12 ohms

Explanation

For two equal resistors in parallel, the combined resistance is half the value of one resistor, so 6 divided by 2 equals 3 ohms. Adding resistances directly applies to series circuits, not parallel ones.

Question 8Physics

Which particle carries a negative charge in an atom?

  1. Neutron
  2. Electron Correct answer.
  3. Proton
  4. Nucleus

Explanation

Electrons orbit the nucleus and each carries a single negative elementary charge. Protons are positive, neutrons are neutral, and the nucleus as a whole is positively charged because of its protons.

Question 9Physics

A block slides down a frictionless incline. Which quantity remains constant during the slide?

  1. The kinetic energy of the block
  2. The total mechanical energy of the block Correct answer.
  3. The potential energy of the block
  4. The speed of the block

Explanation

With no friction, gravity is the only force doing work, so potential energy converts into kinetic energy and the total mechanical energy stays constant. Kinetic energy and speed both increase while potential energy decreases.

Question 10Physics

A force of 20 newtons acts on a 4 kilogram object on a frictionless surface. What is the object's acceleration?

  1. 24 m/s²
  2. 80 m/s²
  3. 0.2 m/s²
  4. 5 m/s² Correct answer.

Explanation

Newton's second law gives acceleration as force divided by mass, so 20 newtons divided by 4 kilograms equals 5 metres per second squared. Multiplying the two quantities or adding them does not follow the law.

Question 11Physics

A wave has a frequency of 50 hertz and a wavelength of 4 metres. What is its speed?

  1. 12.5 m/s
  2. 200 m/s Correct answer.
  3. 0.08 m/s
  4. 54 m/s

Explanation

Wave speed equals frequency multiplied by wavelength, so 50 hertz times 4 metres gives 200 metres per second. Dividing frequency by wavelength or adding the two values does not yield the wave equation result.

Question 12Physics

In a step-down transformer, the ratio of turns in the primary to secondary is 10 to 1. If the primary voltage is 240 volts, what is the secondary voltage?

  1. 24 volts Correct answer.
  2. 240 volts
  3. 120 volts
  4. 2400 volts

Explanation

For an ideal transformer the voltage ratio equals the turns ratio, so the secondary voltage is the primary voltage divided by ten. A step-down transformer reduces voltage while increasing current, keeping power approximately constant.

Question 13Physics

A ball is thrown vertically upward. At the highest point of its flight, which statement about its acceleration is correct?

  1. The acceleration is directed downward at about 9.8 m/s² Correct answer.
  2. The acceleration is zero because the velocity is zero
  3. The acceleration equals the velocity at that instant
  4. The acceleration is directed upward and is maximum

Explanation

Throughout the flight, including at the top, the only force acting is gravity, so the acceleration is constant at about 9.8 metres per second squared downward. Velocity becomes momentarily zero, but acceleration need not be zero when velocity is zero.

Question 14Physics

Which property of a material determines how much it resists the flow of electric current?

  1. Its resistivity Correct answer.
  2. Its refractive index
  3. Its specific heat capacity
  4. Its density

Explanation

Resistance depends on resistivity, length, and cross-sectional area, so resistivity characterises how strongly a material opposes current. Density, specific heat capacity, and refractive index describe entirely different physical properties.

Question 15Physics

A student measures the period of a pendulum ten times and averages the results to reduce random error. This procedure mainly improves:

  1. the zero error of the ruler
  2. the parallax error of the observer
  3. the precision of the measurement Correct answer.
  4. the systematic error of the stopwatch

Explanation

Averaging repeated readings reduces the effect of random fluctuations, improving precision and reducing uncertainty. Systematic errors such as zero error or calibration offset affect all readings equally and are not removed by averaging.

Question 16Physics

An object is placed 30 centimetres from a converging lens of focal length 10 centimetres. Using the lens equation, where is the image formed?

  1. 15 centimetres on the opposite side Correct answer.
  2. 20 centimetres on the opposite side
  3. 7.5 centimetres on the opposite side
  4. 30 centimetres on the same side

Explanation

The lens equation gives one over f equals one over u plus one over v, so one over 10 equals one over 30 plus one over v, giving v equal to 15 centimetres. A positive image distance for a converging lens means a real image on the opposite side.

Question 17Physics

A quantity of heat is supplied to a solid at its melting point. Which statement describes what happens?

  1. The temperature falls as the solid melts
  2. The temperature stays constant while the solid melts Correct answer.
  3. The temperature rises then falls during melting
  4. The temperature rises steadily until the solid melts

Explanation

At the melting point, the supplied energy is used as latent heat to break the bonds of the solid structure rather than to raise kinetic energy. Since temperature reflects average kinetic energy, it remains constant until melting is complete.

Question 18Physics

Two point charges are moved twice as far apart while their charges stay the same. The electrostatic force between them becomes:

  1. half as large
  2. twice as large
  3. one quarter as large Correct answer.
  4. four times as large

Explanation

Coulomb's law states that the force is inversely proportional to the square of the separation. Doubling the distance therefore divides the force by four, giving one quarter of the original value.

Question 19Physics

A radioactive sample has a half-life of 8 days. What fraction of the original nuclei remains after 24 days?

  1. One eighth Correct answer.
  2. One sixth
  3. One third
  4. One half

Explanation

Twenty-four days is three half-lives, since 24 divided by 8 equals 3. Each half-life halves the remaining nuclei, so the fraction left is one half cubed, which is one eighth.

Question 20Physics

A gas is compressed at constant temperature. According to kinetic theory, what happens to the pressure?

  1. It increases because molecules collide with the walls more frequently Correct answer.
  2. It decreases because the molecules slow down
  3. It increases because the molecules become larger
  4. It stays the same because temperature is constant

Explanation

At constant temperature the average kinetic energy of the molecules is unchanged, but the smaller volume means more frequent collisions with the walls per unit area. The greater collision rate raises the pressure, in agreement with Boyle's law.

Question 21Physics

A 2 kilogram ball moving at 3 m/s collides head-on with a stationary 1 kilogram ball and they stick together. What is their common velocity after the collision?

  1. 2 m/s Correct answer.
  2. 6 m/s
  3. 3 m/s
  4. 1 m/s

Explanation

Momentum is conserved in the collision, so the initial momentum of 2 times 3 equals 6 kilogram metres per second is shared by the combined mass of 3 kilograms. Dividing 6 by 3 gives a common velocity of 2 metres per second.

Question 22Physics

A block of mass 5 kilograms is pulled 4 metres along a rough floor by a horizontal force of 30 newtons against a friction force of 10 newtons. What is the net work done on the block?

  1. 40 joules
  2. 80 joules Correct answer.
  3. 120 joules
  4. 200 joules

Explanation

The net horizontal force is 30 minus 10, which equals 20 newtons. Work done by the net force is force times displacement, so 20 newtons times 4 metres gives 80 joules.

Question 23Physics

A satellite orbits Earth in a circular path. Which statement best explains why it does not fall to the surface?

  1. A repulsive force from Earth balances gravity
  2. The satellite is weightless because it is beyond the atmosphere
  3. Gravity does not act on the satellite at that altitude
  4. The satellite's tangential velocity makes it continuously fall around Earth Correct answer.

Explanation

Gravity provides the centripetal force that curves the satellite's path, and its tangential speed is large enough that the curved path matches Earth's curvature. The satellite is in continuous free fall but never reaches the ground because it keeps moving sideways.

Question 24Physics

In a photoelectric experiment, light of frequency above the threshold ejects electrons. If the intensity of the light is doubled while the frequency is unchanged, what happens?

  1. The threshold frequency of the metal increases
  2. No electrons are emitted until the frequency rises further
  3. The number of electrons emitted per second increases Correct answer.
  4. The maximum kinetic energy of the emitted electrons doubles

Explanation

Each photon carries energy determined only by frequency, so the maximum kinetic energy of individual electrons is unchanged. Doubling the intensity doubles the number of photons arriving per second, so more electrons are ejected per second.

Question 25Physics

A wire of resistance R is stretched uniformly so that its length doubles while its volume stays constant. What is its new resistance?

  1. 2R
  2. R/4
  3. 4R Correct answer.
  4. R/2

Explanation

Constant volume means doubling the length halves the cross-sectional area. Resistance equals resistivity times length divided by area, so doubling the length and halving the area multiplies resistance by four.

Question 26Physics

Which of the following is the SI unit of electric charge?

  1. Ampere
  2. Volt
  3. Ohm
  4. Coulomb Correct answer.

Explanation

Electric charge is measured in coulombs, defined as the charge transported by a steady current of one ampere for one second. The volt measures potential difference, the ampere measures current, and the ohm measures resistance, so none of these is the unit of charge.

Question 27Physics

A car travels 150 metres due east and then 200 metres due north. What is the magnitude of its total displacement from the starting point?

  1. 50 metres
  2. 350 metres
  3. 250 metres Correct answer.
  4. 175 metres

Explanation

Displacement is a vector, so the two perpendicular legs form a right triangle whose hypotenuse gives the resultant magnitude. By the Pythagorean theorem, the square root of 150 squared plus 200 squared equals the square root of 62500, which is 250 metres.

Question 28Physics

A body moves with uniform velocity along a straight line. What is the net force acting on it?

  1. A force that increases steadily with time
  2. A constant nonzero force in the direction of motion
  3. Zero Correct answer.
  4. A force directed opposite to the motion

Explanation

Newton's first law states that an object continues in uniform motion unless a net external force acts on it. Uniform velocity means both speed and direction are constant, so acceleration is zero and the net force must also be zero.

Question 29Physics

Which of the following statements about the centre of gravity of a uniform metre rule is correct?

  1. It lies at the 50 centimetre mark Correct answer.
  2. It lies outside the rule
  3. It lies at the 25 centimetre mark
  4. It lies at the 100 centimetre mark

Explanation

For a uniform rod, the mass is distributed evenly, so the centre of gravity coincides with the geometric centre. A metre rule extends from 0 to 100 centimetres, placing the midpoint at the 50 centimetre mark.

Question 30Physics

Which energy conversion takes place in an electric motor?

  1. Chemical energy to electrical energy
  2. Electrical energy to light energy
  3. Mechanical energy to electrical energy
  4. Electrical energy to mechanical energy Correct answer.

Explanation

A current-carrying coil in a magnetic field experiences forces that produce a turning effect, so electrical energy is converted into rotational mechanical energy. The reverse conversion, mechanical to electrical, occurs in a generator.

Question 31Physics

Which type of electromagnetic radiation has the longest wavelength?

  1. Ultraviolet
  2. X-rays
  3. Radio waves Correct answer.
  4. Visible light

Explanation

The electromagnetic spectrum ordered from longest to shortest wavelength runs through radio, microwave, infrared, visible, ultraviolet, X-rays and gamma rays. Radio waves therefore have the longest wavelength and the lowest frequency of the listed types.

Question 32Physics

Which statement correctly describes the pressure at a given depth in a liquid at rest?

  1. It depends only on the depth and the liquid density Correct answer.
  2. It depends on the shape of the container
  3. It decreases as depth increases
  4. It is the same at all depths

Explanation

Hydrostatic pressure equals the product of density, gravitational field strength and depth. It is therefore independent of the container's shape and increases steadily with depth for a given liquid.

Question 33Physics

A thermometer is calibrated using the ice point and steam point of water at standard pressure. Which temperature scale assigns 273 to the ice point?

  1. Rankine
  2. Celsius
  3. Kelvin Correct answer.
  4. Fahrenheit

Explanation

The Kelvin scale is an absolute scale in which the ice point of water at standard pressure is 273 kelvin and the steam point is 373 kelvin. The Celsius scale assigns 0 to the ice point, and Fahrenheit assigns 32.

Question 34Physics

An object of weight 60 newtons rests on a horizontal table. What is the normal reaction force exerted by the table on the object?

  1. 30 newtons upward
  2. Zero, because the object is at rest
  3. 120 newtons upward
  4. 60 newtons upward Correct answer.

Explanation

Since the object is in vertical equilibrium, the upward normal force must balance the downward weight exactly. The normal reaction is therefore 60 newtons directed upward, equal in magnitude to the weight.

Question 35Physics

A car accelerates uniformly from rest to 20 metres per second in 8 seconds. How far does it travel during this time?

  1. 20 metres
  2. 160 metres
  3. 40 metres
  4. 80 metres Correct answer.

Explanation

For uniform acceleration from rest, the average velocity is half the final velocity, namely 10 metres per second. Multiplying this average velocity by the 8 second interval gives a distance of 80 metres.

Question 36Physics

A force of 40 newtons is applied at 60 degrees to a horizontal surface on a block. What is the horizontal component of the force?

  1. 34.6 newtons
  2. 69.3 newtons
  3. 20 newtons Correct answer.
  4. 40 newtons

Explanation

The horizontal component equals the applied force multiplied by the cosine of the angle to the horizontal. Cosine of 60 degrees is 0.5, so the component is 40 times 0.5, which is 20 newtons.

Question 37Physics

Two parallel metal plates separated by a small gap carry equal and opposite charges. Which change increases the capacitance of the arrangement?

  1. Increasing the separation of the plates
  2. Removing the charge from the plates
  3. Reducing the area of the plates
  4. Inserting a dielectric material between the plates Correct answer.

Explanation

Capacitance of a parallel-plate arrangement is proportional to the permittivity of the medium and the plate area, and inversely proportional to the plate separation. Inserting a dielectric raises the permittivity, so the capacitance increases.

Question 38Physics

A current of 0.5 amperes flows through a resistor of 12 ohms. What is the potential difference across the resistor?

  1. 12.5 volts
  2. 0.04 volts
  3. 6 volts Correct answer.
  4. 24 volts

Explanation

Ohm's law states that the potential difference equals current multiplied by resistance. Multiplying 0.5 amperes by 12 ohms gives 6 volts across the resistor.

Question 39Physics

A sound wave travels through air and then enters water, where its speed is greater. Which property of the wave remains unchanged at the boundary?

  1. Wavelength
  2. Amplitude
  3. Speed
  4. Frequency Correct answer.

Explanation

Frequency is determined by the source and is set by the number of oscillations produced each second, so it does not change when the wave crosses into a new medium. Speed changes with the medium, and wavelength adjusts so that speed equals frequency times wavelength.

Question 40Physics

An ideal gas is held at constant volume while its absolute temperature is doubled. What happens to its pressure?

  1. It doubles Correct answer.
  2. It halves
  3. It stays the same
  4. It quadruples

Explanation

At constant volume, pressure is directly proportional to absolute temperature according to the pressure law. Doubling the absolute temperature therefore doubles the pressure, since the molecules strike the walls more often and with greater average momentum change.

Question 41Physics

A convex mirror always forms an image that is which of the following?

  1. Virtual, inverted and magnified
  2. Real, inverted and magnified
  3. Real, upright and diminished
  4. Virtual, upright and diminished Correct answer.

Explanation

A convex mirror diverges incident rays, so the reflected rays only appear to meet behind the mirror, producing a virtual image. This image is always upright and smaller than the object regardless of the object distance.

Question 42Physics

A radioactive source emits alpha particles. Which statement about alpha particles is correct?

  1. They have greater penetrating power than gamma rays
  2. They are high-energy electromagnetic radiation
  3. They are electrons emitted from the nucleus
  4. They are helium nuclei with a charge of plus two Correct answer.

Explanation

An alpha particle consists of two protons and two neutrons, identical to a helium nucleus, and therefore carries a charge of plus two elementary charges. Being relatively massive and charged, alpha particles are stopped by a sheet of paper and are far less penetrating than gamma rays.

Question 43Physics

A spring obeys Hooke's law with a spring constant of 200 newtons per metre. What extension is produced by a stretching force of 10 newtons?

  1. 0.05 metres Correct answer.
  2. 2 metres
  3. 20 metres
  4. 0.5 metres

Explanation

Hooke's law states that the force equals the spring constant multiplied by the extension. Rearranging gives extension equal to force divided by spring constant, so 10 newtons divided by 200 newtons per metre is 0.05 metres.

Question 44Physics

A stone is dropped from a cliff and takes 3 seconds to reach the ground. Taking gravitational field strength as 10 metres per second squared and ignoring air resistance, how high is the cliff?

  1. 45 metres Correct answer.
  2. 30 metres
  3. 90 metres
  4. 15 metres

Explanation

For a body released from rest, the distance fallen equals half the product of gravitational field strength and the square of the time. Half of 10 multiplied by 9 gives 45 metres.

Question 45Physics

A quantity of an ideal gas is taken through a complete cycle and returns to its initial state. What is the net change in its internal energy over the cycle?

  1. Zero Correct answer.
  2. Equal to the net heat absorbed
  3. Equal to the total heat supplied during the cycle
  4. Equal to the net work done by the gas

Explanation

Internal energy is a state function, so it depends only on the current state of the gas. Since the gas returns to its starting state after a complete cycle, the net change in internal energy is zero, and the net heat absorbed equals the net work done.

Question 46Physics

A charged particle enters a uniform magnetic field with its velocity perpendicular to the field. Which statement describes its subsequent motion?

  1. It moves in a circle at constant speed Correct answer.
  2. It moves in a circle with steadily increasing speed
  3. It moves in a straight line at constant speed
  4. It comes to rest immediately

Explanation

The magnetic force on a moving charge is always perpendicular to its velocity, so it does no work and the speed stays constant. A constant force of fixed magnitude acting perpendicular to the velocity provides the centripetal force needed for circular motion.

Question 47Physics

Two coherent sources produce waves that arrive at a point exactly out of phase. What is observed at that point?

  1. A change in the frequency of the waves
  2. Destructive interference with minimum amplitude Correct answer.
  3. Complete reflection of the waves
  4. Constructive interference with maximum amplitude

Explanation

When two coherent waves meet exactly out of phase, their displacements are opposite at every instant and they cancel. This gives destructive interference, so the resultant amplitude is at a minimum at that point.

Question 48Physics

A simple pendulum is taken from Earth to a planet where the gravitational field strength is four times as large. How does its period of small oscillation change?

  1. It becomes half as long Correct answer.
  2. It becomes four times as long
  3. It stays the same
  4. It becomes twice as long

Explanation

The period of a simple pendulum is proportional to the square root of the length divided by gravitational field strength. Quadrupling the field strength reduces the square root factor by two, so the period becomes half as long.

Question 49Physics

A block of mass 2 kilograms moving at 4 metres per second collides with and sticks to a stationary block of mass 6 kilograms. What fraction of the original kinetic energy is lost in the collision?

  1. One quarter
  2. One half
  3. None of the energy
  4. Three quarters Correct answer.

Explanation

By conservation of momentum, the combined speed after the perfectly inelastic collision is 8 divided by 8, which is 1 metre per second. The initial kinetic energy is 16 joules while the final is 4 joules, so 12 joules, or three quarters, is lost.

Question 50Physics

A uniform wire of resistance 8 ohms is bent into a closed circle, and a battery is connected across two points that divide the circle into arcs of one quarter and three quarters of the circumference. What is the resistance of the network between these two points?

  1. 6 ohms
  2. 2 ohms
  3. 8 ohms
  4. 1.5 ohms Correct answer.

Explanation

The two arcs act as resistors in parallel with values of 2 ohms and 6 ohms, since resistance is proportional to length. Their parallel combination is the product divided by the sum, giving 12 divided by 8, which is 1.5 ohms.