NDA Examination Physics (General Ability Test - General Knowledge) Syllabus

Define mechanical advantage of a simple machine.

Mechanical advantage = load / effort; it is the factor by which a machine multiplies the input force.

Define pressure and state its SI unit. State Pascal's law.

Pressure is force per unit area, P = F/A; SI unit is the pascal (Pa = N/m^2). Pascal's law: pressure applied to an enclosed fluid is transmitted equally in all directions.

State Archimedes' principle.

A body immersed wholly or partly in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.

What is the difference between heat and temperature?

Heat is the total thermal energy transferred due to temperature difference (in joules); temperature measures the average kinetic energy of particles (in kelvin/celsius).

Convert 100 degrees Celsius to Kelvin and to Fahrenheit.

100 C = 373.15 K = 212 F.

Define specific heat capacity and give its SI unit.

Specific heat capacity is the heat required to raise the temperature of 1 kg of a substance by 1 K (or 1 C). SI unit: J/(kg K).

What are the three modes of heat transfer? Define each briefly.

Conduction (heat through a medium by particle vibration, no bulk movement), convection (heat by actual movement of fluid particles), radiation (heat by electromagnetic waves, no medium needed).

By which mode of heat transfer does the Sun's heat reach the Earth, and why?

By radiation, because the space between the Sun and Earth is a vacuum and radiation requires no medium.

Why are cooking utensils given black bottoms and shiny tops?

Black surfaces are good absorbers of radiant heat (faster heating), while shiny surfaces are poor radiators/absorbers (reduce heat loss).

Define latent heat. What is latent heat of fusion and of vaporization?

Latent heat is the heat absorbed or released during a change of state at constant temperature. Latent heat of fusion accompanies solid-liquid change; latent heat of vaporization accompanies liquid-gas change.

Name the change of state processes: solid to liquid, liquid to gas, solid to gas, and gas to liquid.

Solid to liquid = melting (fusion); liquid to gas = vaporization (boiling/evaporation); solid to gas = sublimation; gas to liquid = condensation.

Why does the temperature of water remain constant while it is boiling, despite continued heating?

The supplied heat is used as latent heat of vaporization to change the state from liquid to gas rather than raising the temperature.

State the laws of reflection of light.

1) The angle of incidence equals the angle of reflection. 2) The incident ray, reflected ray, and normal at the point of incidence all lie in the same plane.

What type of image is formed by a plane mirror?

A virtual, erect image of the same size as the object, laterally inverted, formed as far behind the mirror as the object is in front.

Define refraction of light and state Snell's law.

Refraction is the bending of light as it passes between media of different optical densities. Snell's law: n1 sin(i) = n2 sin(r), or refractive index n = sin(i)/sin(r).

What is total internal reflection and one condition for it to occur?

Total internal reflection occurs when light traveling from a denser to a rarer medium is completely reflected back; it requires the angle of incidence to exceed the critical angle.

What type of lens is used to correct myopia (short-sightedness) and hypermetropia (long-sightedness)?

Myopia is corrected with a concave (diverging) lens; hypermetropia is corrected with a convex (converging) lens.

Name the part of the human eye that controls the amount of light entering, and the part where the image is formed.

The iris (with the pupil) controls light entering; the image is formed on the retina.

What is the power of a lens, its unit, and the formula relating it to focal length?

Power is the ability of a lens to converge or diverge light; unit is the dioptre (D). P = 1/f, with focal length f in metres.

What is dispersion of light? Give the order of colours in the spectrum of white light.

Dispersion is the splitting of white light into its constituent colours by a prism. The order is VIBGYOR: violet, indigo, blue, green, yellow, orange, red.

In dispersion, which colour bends the most and which bends the least?

Violet bends the most (shortest wavelength); red bends the least (longest wavelength).

How is a rainbow formed?

A rainbow forms by refraction, total internal reflection, and dispersion of sunlight by water droplets in the atmosphere.

Sound is what type of wave, and can it travel through a vacuum?

Sound is a longitudinal mechanical wave; it cannot travel through a vacuum because it needs a material medium.

What is the audible frequency range for humans? Define ultrasonic and infrasonic.

The audible range is about 20 Hz to 20,000 Hz. Ultrasonic = above 20,000 Hz; infrasonic = below 20 Hz.

Define an echo. What minimum time gap and distance are required to hear one?

An echo is the reflection of sound back to the listener. It requires a time gap of at least 0.1 s, meaning the reflecting surface must be at least about 17 m away.

State Ohm's law and its formula.

At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V = IR.

Write the formula for the equivalent resistance of resistors in series and in parallel.

Series: R = R1 + R2 + R3 + ... ; Parallel: 1/R = 1/R1 + 1/R2 + 1/R3 + ...

What is the difference between AC and DC current?

Direct current (DC) flows in one constant direction; alternating current (AC) periodically reverses direction. Indian mains supply is AC at 50 Hz.

State the rule that gives the direction of magnetic field around a current-carrying straight conductor.

The right-hand thumb rule (Maxwell's corkscrew rule): point the thumb along the current and the curled fingers show the direction of the magnetic field lines.

What is electromagnetic induction, and which device works on this principle to generate electricity?

Electromagnetic induction is the production of an EMF/current in a conductor by a changing magnetic field (Faraday's law). The electric generator (dynamo) works on this principle.