Std. 10
Physics

The turning effect of a force about a fixed point is called moment or torque. It depends on the force and its perpendicular distance from the pivot.

Moment = Force × perpendicular distance from pivot . Clockwise and anticlockwise moments must be considered with their directions.

A body is in translational equilibrium when the resultant force is zero. For rotational equilibrium, the clockwise and anticlockwise moments about a suitable point balance.

The centre of gravity is the point through which the entire weight of a body may be considered to act. Its position depends on the distribution of mass.

W = Fs cos θ. Work is done when a force produces displacement. At θ=0°, W=Fs; at θ=90°, work done is zero.

Energy is the capacity to do work. Gravitational potential energy: U=mgh; translational kinetic energy: K=½mv².

P=W/t. Power tells how quickly work is done. SI unit is watt; 1 hp = 746 W.

Energy cannot be created or destroyed; it changes from one form to another. For a freely falling body, the decrease in potential energy appears as kinetic energy, so total mechanical energy remains constant when losses are neglected.

Machines make work more convenient or act as force multipliers. MA=L/E VR=distance moved by effort/distance moved by load η=MA/VR ×100%. For practical machines, efficiency is less than 100% and MA

Refraction is the change in direction of light when it passes obliquely from one transparent medium to another because its speed changes.

The incident ray, refracted ray and normal lie in the same plane. For a given pair of media, the ratio of sine of angle of incidence to sine of angle of refraction is constant.

μ = sin i / sin r = speed of light in vacuum / speed of light in medium. A higher refractive index generally means lower speed of light in that medium.

An object under water viewed from air appears raised because of refraction. This apparent depth is smaller than the real depth for normal viewing.

When light travels from a denser to a rarer medium, there is a critical angle at which the refracted ray grazes the boundary. For incidence greater than the critical angle, total internal reflection occurs.

Optical fibres, prisms and some optical instruments use refraction or total internal reflection. The path of rays must be drawn with a normal and correct angles.

A convex lens is thicker at the centre and converges parallel rays; a concave lens is thinner at the centre and diverges parallel rays.

For a convex lens, parallel rays converge at the principal focus. For a concave lens, parallel rays appear to diverge from a virtual principal focus.

1/f = 1/v − 1/u using the Cartesian sign convention. Always assign signs to u, v and f before substitution.

m = v/u = hᵢ/hₒ. The sign and magnitude tell whether the image is inverted/upright and enlarged/reduced under the adopted convention.

P=1/f(metre). The unit is dioptre (D). A converging lens has positive power and a diverging lens has negative power.

Use the standard principal rays: parallel-to-axis ray, ray through optical centre and ray through/following the principal focus. The intersection or apparent intersection gives the image.

Dispersion is splitting of white light into its component colours when it passes through a prism because different wavelengths are refracted by different amounts.

The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. They travel at the same speed in vacuum but differ in wavelength and frequency.

Visible light occupies a small range between infrared and ultraviolet. Different wavelengths are perceived as different colours.

Infrared is associated with thermal imaging and remote controls; ultraviolet can cause fluorescence and is used for sterilisation; X-rays are used for imaging; radio waves are used for communication.

Sound is produced by vibrating bodies and requires a material medium for propagation. In air it travels as a longitudinal wave of compressions and rarefactions.

Frequency determines pitch; amplitude is related to loudness; waveform affects quality or timbre. v=fλ.

An echo is reflected sound heard separately from the original when the time gap is sufficient. The distance can be related to speed and round-trip time.

Resonance occurs when a system is forced at or near its natural frequency, producing a large amplitude of vibration.

Ultrasound has frequency above the human audible range. It is used in medical imaging, industrial testing and other applications.

Current is rate of flow of charge: I=Q/t. Its SI unit is ampere.

Potential difference is work done per unit charge: V=W/Q. It provides the electrical driving effect in a circuit.

For a conductor at constant physical conditions, V=IR. Resistance measures opposition to current.

For a uniform conductor, R=ρl/A, where ρ is resistivity, l length and A cross-sectional area.

In series, resistances add: R=R₁+R₂+…. For parallel resistors, 1/R=1/R₁+1/R₂+….

P=VI=I²R=V²/R. Electrical energy is E=Pt; commercial electrical energy is commonly measured in kWh.

Domestic appliances are connected in parallel so each receives the supply voltage independently. Fuse/MCB protection and earthing help reduce electrical hazards.

A magnetic field is the region where a magnetic pole or current-carrying conductor experiences magnetic force.

The magnetic field around a straight current-carrying conductor forms concentric circles. Direction is found using the right-hand thumb rule.

A current-carrying coil produces a magnetic field. A soft iron core can strengthen it, producing an electromagnet whose magnetism can be switched on and off.

A current-carrying conductor placed in a magnetic field experiences a force. This is the working principle of an electric motor.

A changing magnetic flux through a conductor can induce an emf and current. This is the basis of generators and transformers.

A generator converts mechanical energy into electrical energy by electromagnetic induction. The direction of induced current depends on the direction of motion and magnetic field.

Temperature indicates the degree of hotness and relates to average thermal motion; heat is energy transferred because of a temperature difference.

Q=mcΔT. Specific heat capacity is the heat required to raise the temperature of unit mass of a substance by one degree.

During a change of state, temperature remains constant while heat is absorbed or released. Q=mL.

The principle of calorimetry is conservation of heat: under ideal conditions, heat lost by the hotter body equals heat gained by the colder body.

Melting changes solid to liquid; boiling changes liquid to gas; condensation and freezing are reverse processes. Latent heat is involved without temperature change during the state change.

Radioactivity is spontaneous emission of radiation from unstable atomic nuclei. It is a nuclear phenomenon and is not significantly affected by ordinary chemical changes.

Alpha particles are helium nuclei, beta radiation consists of high-speed electrons or positrons depending on the decay, and gamma radiation is high-energy electromagnetic radiation. Their penetrating and ionising powers differ.

Radioactive decay changes the nucleus and may transform one element into another. Nuclear equations must conserve mass number and atomic number.

Half-life is the time required for half of the radioactive nuclei in a sample to decay. After n half-lives, the remaining fraction is (1/2)ⁿ.

Radioisotopes have medical, industrial and scientific uses. Radiation can damage living tissue, so shielding, distance, exposure time and proper handling are important.

Fission is splitting of a heavy nucleus into lighter nuclei with release of energy. A chain reaction can occur when emitted neutrons cause further fissions.

Fusion combines light nuclei to form a heavier nucleus and can release large amounts of energy. Extremely high temperatures are required to overcome electrostatic repulsion.

Mass and energy are related by E=mc². A small mass difference can correspond to a large energy release because c² is very large.

Nuclear reactors control fission to release heat, which is converted into electrical energy. Safety systems and management of radioactive waste are essential.

Fission uses heavy nuclei and can sustain a controlled chain reaction; fusion uses light nuclei and requires extreme conditions. Both are nuclear rather than chemical energy processes.

Use SI units unless the question specifies otherwise. Record measurements with appropriate precision and use correct instrument readings.

Choose suitable scales, label axes with quantities and units, plot points accurately and draw a smooth or best-fit line when appropriate.

The ICSE course includes practical verification such as moments, electrical measurements, refraction, lenses and calorimetry. The student should know the apparatus, procedure, observation, calculation and source of error.

Use a ruler, draw the principal axis and normal where needed, and mark angles and image positions clearly.

Write the given quantities, convert units, select the relevant formula, substitute with signs/units and state the final answer with its unit.