# Investigatory Project in Physics for Class 10

PROJECT 1: THE EMISSIVE POWER AND EMISSIVITY

Aim:

To study the emissive power and emissivity of a surface for different colours)

Materials and apparatus:

(i) Tin cans of same size with their outer surfaces including lids painted with different colours like black, white, red, etc.

(ii) Sensitive thermometer with least count 0.1 °C.

(iii) Stand, water etc.

Procedure

The surface area A of a can is determined by measuring its dimension using vernier calipers. Its mass m1 and the mass m2 of water completely filling the can are determined. Specific heat capacity c of the material of the tin is noted from the standard tables. The black coloured tin can is filled with hot water at a temperature above 90 °C. It suspended from a stand. The temperature of water is noted by a thermometer. When its temperature falls to 90°C, a stopwatch is started. Temperatures of water are noted after every 30 seconds. The time-temperature observation is taken till the temperature falls to, say, 70°C. A graph is drawn with temperature θ along the Y-axis and time t along the X-axis.

From the graph the rate of cooling at a temperature θ = dθ/dt = AB/BC, is determined.

Quantity of heat lost in one second by the tin can and water at a given temperature θ is calculated by the equation,

Q = (m1c1 + m2c2)(dθ/dt)θ

The emissive power e is calculated from the relation, e = Q/A.

The experiment is repeated for the tin can of different colours.

Emissivity of a surface of for a given colour = (emissive power of the surface for the given colour)/ (emissive power of the black surface)

PROJECT 2: THE THERMOELECTRIC THERMOMETER

Aim:

To construct a thermoelectric thermometer using copper and iron and to calibrate it using digital multimeter

Materials and Apparatus:

(i) Copper and iron wires

(ii) Digital multimeter with low voltage range

(iii) Thermometer

(iv) Two beakers containing melting ice

Procedure:

To construct a thermoelectric thermometer, two dissimilar metal wires, Cu and Fe, are joined together to form a thermocouple. A digital multimeter V at the low voltage range is connected as shown in the figure. The wires should not touch each other except at their ends.

Both the junction of the thermocouple are kept in melting ice at 0°C taken in two beakers. The reading of the voltmeter is taken. It will be zero. One of the beakers containing the ice is heated. The junction of the couple in this beakers is the hot junction. The temperature of the hot junction is kept at 10°C, 20°C, ... 100°C and the corresponding voltmeter readings are noted.

A calibration curve is drawn with thermo-emf V in mV along the Y-axis and temperature of hot junction θ in °C along the X-axis.

To find the unknown temperature of a bath, the hot junction is kept immersed in the bath and the voltmeter reading is noted. From the calibration curve, the unknown temperature can be determined.

PROJECT 3: THE HOT WIRE AMMETER

Aim:

To construct a hot wire ammeter, calibrate it and measures the current in a circuit (both ac and dc)

Material and Apparatus:

(i) A uniform resistance wire

(ii) Helical spring

(iii) A step down transformer

(iv) A plug and wire

(v) dc source (battery eliminator)

(vi) Wooden board

(vii) Long screws

(viii) Thin flat straight pointed strip with holes at flat end and the mid-point

(ix) A card-board cut in the shape of a protractor.

Procedure

Two screws A and B are fixed at a distance of about 20 cm apart on a wooden board kept horizontally. A resistance wire is kept stretched and firmly tied to A and B. The ends of the wire are connected to two terminals T1 and T2 using connecting wires. A third screw C is fixed on the board along the perpendicular bisector of AB. A helical spring S is stretch between the centre O of the string and the screw C. One end of the pointer is fixed to the end of the spring at O by slipping the end of the spring through the hole in the pointer. The pointer is pivoted at its centre H. The pointer is so pivoted that it turn from the left to the right on the circular scale as the string is pulled by the spring. The extreme left position of the pointer is marked as zero on the scale.

When current is passed through the wire, the wire heat up and expands linearly. Since it is pulled by the spring, it sags and the pointer moves over the scale.

To calibrate the scale, the dc source is connected in series with a rheostat, dc ammeter and a key between T1 and T2. Using known currents calibrate the scale. (The current should be sufficiently large to get appreciable deflection of the pointer). The ac from the main (230 V) is stepped down by a low voltage step down transformer. To measure the unknown current of ac, it is connected in series with the terminals T1 and T2 through a rheostat. The reading of the pointer on the scale gives the rms value of the current.

PROJECT 4: THE ELASTIC HYSTERESIS

Aim:

To study the hysteresis of rubber

Material and apparatus required :

A long rubber band in the form of a loop, stand, weight hanger, slotted weights, metre scale, thin long pointer etc.

Procedure

The rubber band R which is in the form of a loop is suspended from a stand. The weight hanger with a dead weight w0 is suspended from the loop by slipping the hook of the weight hanger on to the lower end of the loop. The pointer P is fixed horizontally to the upper end of the weight hanger using plasticine (a type of gum). The metre scale S is fixed vertically such that the pointer is just infront of the scale readings.

The initial reading r0 of the pointer is noted with the dead weight w0. A slotted weight m gwt is placed on the dead weight. The reading r1 of the pointer is taken again. The difference in readings r1 – r0 gives the extension e for a load M = 1m. Similarly the extensions e for the loads M = 2m, 3m, 4m…… are noted.