The activity of a radioactive substance depends on
The activity of a radioactive substance depends on its purity (proportion of radioactive isotopes) and age (due to decay over time), but not on temperature or pressure.
The SI unit of force is
The SI unit of force is the newton (N), defined as kg·m/s², derived from Newton’s second law (F = ma).
A body moves with a constant speed of 10 m/s for 5 s. The distance covered is
Distance = speed × time = 10 m/s × 5 s = 50 m.
The tendency of a body to remain at rest or in uniform motion is called
Inertia is the property of a body to resist changes to its state of rest or uniform motion, as per Newton’s first law.
A car accelerates uniformly from rest at 2 m/s² for 4 s. Its final velocity is
Using v = u + at, where u = 0, a = 2 m/s², t = 4 s: v = 0 + 2 × 4 = 8 m/s.
The work done by a force of 20 N moving an object 5 m in the direction of the force is
Work = force × distance = 20 N × 5 m = 100 J.
The principle of conservation of energy states that energy
The law of conservation of energy states that energy cannot be created or destroyed, only transformed.
A machine with a velocity ratio of 5 requires 200 J of work to lift a load. The work done by the effort is
For an ideal machine, work input equals work output. Thus, the effort does 200 J of work to lift the load.
The unit of power is
Power is the rate of doing work, measured in watts (W), where 1 W = 1 J/s.
A projectile is launched horizontally. The factor that primarily determines its time of flight is
For horizontal projection, time of flight depends on the height and gravitational acceleration, as t = √(2h/g).
The specific heat capacity of a substance is the heat required to raise the temperature of
Specific heat capacity is the heat needed to raise 1 kg of a substance by 1 K, measured in J/kg·K.
The boiling point of water is affected by
Impurities, such as salt, raise the boiling point of water by altering its vapor pressure.
The process by which a gas changes directly to a solid is called
Deposition is the direct transition from gas to solid, such as frost forming on a cold surface.
A gas occupies 2 m³ at 27 °C. If the temperature is raised to 127 °C at constant pressure, the new volume is
Using Charles’ law (V₁/T₁ = V₂/T₂), T₁ = 27 + 273 = 300 K, T₂ = 127 + 273 = 400 K, V₁ = 2 m³. Thus, V₂ = (400/300) × 2 = 2.4 m³.
A 500 g block of iron at 100 °C is placed in 1 kg of water at 20 °C. Assuming no heat loss, the final temperature is closest to (specific heat of iron = 450 J/kg·K, water = 4200 J/kg·K)
Heat lost by iron = heat gained by water. m₁c₁(T₁ - T) = m₂c₂(T - T₂). Substituting: 0.5 × 450 × (100 - T) = 1 × 4200 × (T - 20). Solving gives T ≈ 25 °C.
The speed of sound in air is approximately
The speed of sound in air at standard conditions (20 °C) is approximately 330 m/s.
The phenomenon of light bending as it passes from one medium to another is called
Refraction is the bending of light due to a change in speed when moving between media with different refractive indices.
The image formed by a plane mirror is
A plane mirror forms a virtual, upright image that appears behind the mirror, at the same distance as the object.
The frequency of a wave is 50 Hz, and its wavelength is 2 m. The speed of the wave is
Wave speed = frequency × wavelength = 50 Hz × 2 m = 100 m/s.
The primary colors of light are
The primary colors of light are red, green, and blue, which combine to produce all other colors in the visible spectrum.
The SI unit of electric current is
The ampere (A) is the SI unit of electric current, measuring the flow of charge per unit time.
Ohm’s law is expressed as
Ohm’s law states that voltage (V) equals current (I) times resistance (R), or V = IR.
Two resistors of 4 Ω and 6 Ω are connected in parallel. The equivalent resistance is
For parallel resistors, 1/R_eq = 1/R₁ + 1/R₂ = 1/4 + 1/6 = 3/12 + 2/12 = 5/12. Thus, R_eq = 12/5 = 2.4 Ω.
The power dissipated in a 5 Ω resistor with a 10 V potential difference is
Power = V²/R = 10²/5 = 100/5 = 20 W.
A current of 2 A flows through a conductor for 10 s. The charge that passes through is
Charge = current × time = 2 A × 10 s = 20 C.
The device used to step up or step down voltage in an AC circuit is a
A transformer changes the voltage in an AC circuit by electromagnetic induction.
The direction of the magnetic field around a current-carrying conductor is determined by
The right-hand rule determines the magnetic field direction: thumb along current, fingers curl in the field’s direction.
The force on a charge moving in a magnetic field is maximum when the angle between the velocity and field is
The force F = qvB sinθ is maximum when sinθ = 1, i.e., θ = 90°.
The device that converts AC to DC is called a
A rectifier converts alternating current (AC) to direct current (DC) using diodes.
The energy stored in a capacitor is given by
The energy stored in a capacitor is ½CV², where C is capacitance and V is voltage.
The particle emitted during alpha decay is
An alpha particle is a helium nucleus (²⁴He), emitted during alpha decay.
The half-life of a radioactive substance is the time taken for
Half-life is the time for half the radioactive nuclei in a sample to decay.
The energy of a photon is proportional to its
Photon energy is given by E = hf, where h is Planck’s constant and f is frequency.
The process by which a nucleus splits into two smaller nuclei is
Nuclear fission is the splitting of a heavy nucleus into two smaller nuclei, releasing energy.
The particle responsible for the strong nuclear force is the
Gluons mediate the strong nuclear force, binding quarks within protons and neutrons.
The photoelectric effect demonstrates that light behaves as
The photoelectric effect shows light acting as particles (photons), ejecting electrons from a metal surface.
The de Broglie hypothesis suggests that particles have
De Broglie proposed that particles, like electrons, exhibit wave-like properties, with wavelength λ = h/p.
The binding energy of a nucleus is the energy
Binding energy is the energy needed to separate a nucleus into its individual protons and neutrons.
The device used to detect radiation is a
A Geiger counter detects ionizing radiation, such as alpha, beta, or gamma rays.
Einstein’s mass-energy equivalence is expressed as
Einstein’s equation E = mc² relates energy (E) to mass (m) and the speed of light (c) squared.
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