Physics

If you place a ball on a flat surface, it will remain there until unless you disturb it. It will move only when either we push it or pull it. This push or pull acting on an object is known as a force. At least two objects must interact for a force to come into play. An interaction of one object with another object results in a force between the two objects.

In ancient times, the length of a foot, the width of a finger, and the distance of a step were commonly used as different units of measurements. In 1790, the French created a standard unit of measurement called the metric system.  For the sake of uniformity, scientists all over the world have accepted a set of standard units of measurement. The system of units now used is known as the International System of Units (SI units).

Experiment: To determine the internal resistance of a galvanometer by half deflection method, and to convert it into a volt meter of a given range, say (0-3 V), and verify it.

Experiment: To draw the lines of force due to a bar magnet keep (i) N-pole pointing to magnetic north of the earth (ii) S-pole pointing to magnetic north of the earth. Locate neutral points.

Experiment: To draw the characteristics of an NPN transistor in common emitter mode. From the characteristics find out (i) the current gain (β) of the transistor and (ii) the voltage gain A_V with a load resistances of 1k Ω.

Experiment: To draw the characteristic curve of a forward biased pn junction diode and to determine the static and dynamic resistance of the diode.

Experiment: Study decay of current in a RC circuit while charging the capacitor, using a galvanometer and find the time constant of the circuit.

Experiment: Determine the inductance and resistance of a given coil (inductor) using a suitable series resistance and an AC voltmeter.

Experiment: Determine the internal resistance of a primary cell using a potentiometer.

Experiment: Determine the specific resistance of the material of two given wires using a metre bridge.

Experiment: To compare the e.m.f.’s of two given primary cells by using a potentiometer.

Experiment: To verify the law of combination (series and parallel) of resistances using ammeter - voltmeter method and coils of known resistances.

Experiment: To set up an astronomical telescope and find its magnifying power.

Experiment: To compare the refractive indices of two transparent liquids using a concave mirror and a single pin.

When the object is placed on the centre of curvature of the concave mirror, the real inverted image is formed at the centre of curvature (i.e. at the same point).

Experiment: To draw a graph between the angle of incidence (i) and angle of deviation (δ) for a glass prism and to determine the refractive index of the glass of the prism using this graph.

Experiment: Determine the focal length of a concave lens by combining it with a suitable convex lens.

Experiment: Find the focal length of a convex mirror using a convex lens.

A convex mirror always forms virtual image of a real object and hence the value of v (i.e. the position of the image) cannot be obtained directly. Therefore, convex lens is used to enable us to form a real image due to the combination.

Experiment: To find the focal length (f) of a convex lens by plotting graph between 1/u and 1/v.

Experiment: To find the value of v for different values of u in case of a concave mirror and find its focal length (f) by plotting graph between 1/u and 1/v.

Experiment: To establish graphically the relation between the tension and length of the string of a sonometer resonating with a given tuning fork. Use the graph to determine the mass per unit length of the string.

Experiment: To compare the frequencies of two tuning forks by finding the first and second resonance positions in a resonance tube.

Experiment: To determine (i) the wavelength of sound produced in an air column, (ii) the velocity of sound in air at room temperature using a resonance column and a tuning fork.

Experiment: To find the time required to empty a burette, filled with water, to ½ of its volume, to ¼ of its volume, to 1/8 of its volume and so on. Then plot a graph between volume of water in the burette and time and thus study at each stage that the fractional rate of flow is same (analogy to radio-active decay).

Experiment: To measure extensions in the length of a helical spring with increasing load.

Experiment: Determine the specific heat of a solid using the method of mixtures.

Specific heat:  The amount of heat required for a unit mass of substance to raise its temperature by 1°C is defined as specific heat.

Experiment: To study the Newton’s law of cooling by plotting a graph between cooling time and temperature difference between calorimeter and surroundings.

Experiment: To find the weight of a given body using law of parallelogram of vectors.

According to Newton’s Third Law of motion, tension in a string supporting a body is equal to the weight of the body.

Experiment: Determine the radius of curvature of a concave mirror using a spherometer.

Experiment: Determine the diameter of a given wire using a screw gauge.

Pitch: The pitch of the screw is the distance through which the screw moves along the main scale in one complete rotation of the cap on which is engraved the circular scale.

Experiment: Determine the internal diameter and depth of a cylindrical container (like tin can, calorimeter) using a vernier callipers and find its capacity. Verify the result using a graduated cylinder.

Experiment: To find the time period of a simple pendulum for small amplitudes and draw the graph of length of pendulum against square of the time period. Use the graph to find the length of the second’s pendulum.

Critical Velocity

When the velocity of flow is less than a certain value, called critical velocity, the flow remains streamlined. But when the velocity of flow exceeds the critical velocity, the flow becomes turbulent.

While waiting on a railway platform for the arrival of a train, you might have observed that the pitch of the whistle when the engine approaches you and when the engine moves away from you are different. The pitch is higher when the engine approaches but is lower when the engine moves away.

Maxwell gave the idea of e.m. waves while Hertz, J.C. Bose, Marconi and others successfully produced such waves of different wavelengths experimentally. However, in all the methods, the source of e.m. waves is the accelerated charge.

Electromagnetic waves are transverse in nature.

They consist of electric (E) and magnetic fields (B) oscillating at right angles to each other and perpendicular to the direction of propagation (k).

It is the simplest form of a wind instrument. A wooden or metal pipe producing musical sound is known as organ pipe. Flute is an example of organ pipe.

The characteristics of musical sounds help to distinguish one musical sound from another. These are pitch, londness and quality.

Travelling Waves

1. Particular conditions of the medium namely crests and troughs or compressions and rarefactions appear to travel with a definite speed depending on density and elasticity (or tension) of the medium.

The equation of a simple harmonic wave travelling with velocity v = ω/k in a medium is

y₁ = – a sin (ωt – kx)

Initially, at t = 0, the incident wave and the reflected wave are in the opposite phases. Hence the resultant displacement at each point is zero. All the particles are in their respective mean positions.

Superposition of waves of same frequency propagating in the same direction produces interference. The outcome of superposition of waves of nearly the same frequency is beats.

Consider two simple harmonic waves of amplitudes a₁ and a₂ each of angular frequency ω, both propagating along x-axis, with the same velocity v = ω/k but differing in phase by a constant phase angle φ.

The modulated carrier waves are beamed by a transmitter directly towards the satellite. The satellite receiver amplifies the received signal and re-transmits it to earth at a different frequency to avoid interference.

Very high antennas are used at radio station. These are used for broadcasting.

In ground wave propagation, the electromagnetic waves travel along the surface of the earth. These can bend around the corners of the objects but are affected by terrain.

In sky wave or ionospheric propagation, the electromagnetic waves of frequencies between 3 MHz – 30 MHz launched by a transmitting antenna travel upwards, get reflected by the ionosphere and return to distant locations.

The wireless communication between a transmitting and a receiving station utilizing the space around the earth, i.e. atmosphere is called space communication.

The 1960 invention of the laser (Light Amplification by Stimulated Emission of Radiation) completely revolutionized communication technology. The laser, which is a highly coherent source of light waves, can be used as an enormously high capacity carrier wave for information carrying signals (voice, data or video) transmitted through an optical wave guide, such as an optical fibre.

For guided signal transmission, a transmission line, a material medium forms a path. The construction of a transmission line determines the frequency range of the signal that can be passed through it. Fig. 32.1 shows some typical transmission lines.

The modulated signal carrying the information, once radiated by the antenna, travels in space. Since there are so many transmitting stations, thousands of signals reach the antenna.