Physics Practical Notes PDF

EXPERIMENT NO. 1 METRE BRIDGE - 1 Aim: To find the resistance of a given wire using metre bridge. Materials Required: A metre bridge, Leclanche cell, galvanometer, resistance box, jockey, one-way key, resistance wire, metre scale, connecting wires and a piece of sa...

EXPERIMENT NO. 1 METRE BRIDGE - 1 Aim: To find the resistance of a given wire using metre bridge. Materials Required: A metre bridge, Leclanche cell, galvanometer, resistance box, jockey, one-way key, resistance wire, metre scale, connecting wires and a piece of sandpaper. Theory: Metre bridge apparatus is also known as a slide wire bridge. It works on the principle of Wheatstone’s bridge. It is fixed on the wooden block and consists of one-metre- long wire with a uniform cross-sectional area. It has two gaps formed using thick metal strips to make the Wheatstone’s bridge. 𝑅 𝑙 𝑅(100−𝑙) According to Wheatstone’s principle, 𝑋 = 100−𝑙 𝑜𝑟, 𝑋= 𝑙 Procedure: The arrangement of the apparatus should be as shown in the circuit diagram. The wire whose resistance is to be determined should be connected in the right gap between B and C without any formation of loops. The resistance box should be connected in the left gap between A and B. All the other connections should be as shown in the circuit diagram. Introduce 1-ohm resistance in the resistance box. The jockey should be first touched gently to the left end and then to the right end of the bridge. The deflections in the galvanometer should be in opposite directions. Note the galvanometer deflection. Let D be the null point where the jockey is touching the wire. Take a resistance from the resistance box, such that when the jockey is nearly in the middle of the wire, there shouldn’t be any deflection in the galvanometer. Note the position of D to know the length of AD = 𝑙 𝑐𝑚. Calculate the value of X, using the 𝑅(100−𝑙) formula, 𝑋 = 𝑙 Four sets of observations should be taken by changing the value of R. Record the observations in a tabular form. Calculate the mean value of X. Result: The value of unknown resistance X = …….ohm Precautions: 1. The connections should be neat, tight and clean. 2. Plugs should be tightly connected in the resistance box. 3. The movement of the jockey should be gentle, and it shouldn’t be rubbed. 4. The null point should be between 40 cm and 60 cm. Sources of Error: 1. The screws of the instrument might be loose. 2. The wire might not be of uniform diameter. 3. Parallax error Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 1 Circuit Diagram: Observation table Sr. No. Resistance Length, 𝑨𝑫 = Length 𝑫𝑪 = (𝟏𝟎𝟎 − Unknown Resistance R (Ohm) 𝒍(cm) 𝒍) (cm) 𝑹 (𝟏𝟎𝟎−𝒍) 𝑿= (ohm) 𝒍 1 2 3 4 5 Calculations: 𝑹(𝟏𝟎𝟎−𝒍) Unknown resistance of the given wire is calculated using the formula, 𝑿 = 𝒍 1. 2. 3. 4. 5. Mean value of X = EXPERIMENT NO. 2 METRE BRIDGE - 2 Aim: To verify the laws of combination of resistances in series using metre bridge. Materials Required: A metre bridge, Leclanche cell, galvanometer, resistance box, jockey, one-way key, resistance wires, metre scale, connecting wires and a piece of sandpaper. Theory: Metre bridge apparatus is also known as a slide wire bridge. It works on the principle of Wheatstone’s bridge. It is fixed on the wooden block and consists of one-metre- Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 2 long wire with a uniform cross-sectional area. It has two gaps formed using thick metal strips to make the Wheatstone’s bridge. 𝑅 𝑙 𝑅(100−𝑙) According to Wheatstone’s principle, 𝑋 = 100−𝑙 𝑜𝑟, 𝑋= 𝑙 Procedure: The arrangement of the apparatus should be as shown in the circuit diagram. The wire r1 whose resistance is to be determined should be connected in the right gap between B and C without any formation of loops. The resistance box should be connected in the left gap between A and B. All the other connections should be as shown in the circuit diagram. Introduce 1-ohm resistance in the resistance box. The jockey should be first touched gently to the left end and then to the right end of the bridge. The deflections in the galvanometer should be in opposite directions. Note the galvanometer deflection. Let D be the null point where the jockey is touching the wire. Take a resistance from the resistance box, such that when the jockey is nearly in the middle of the wire, there shouldn’t be any deflection in the galvanometer. Note the position of D to know the length of AD = 𝑙 𝑐𝑚. Calculate the value of 𝑅(100−𝑙) r1, using the formula, 𝑟1 = Three sets of observations should be taken by changing 𝑙 the value of R. Record the observations in a tabular form. Repeat the experiment using the wire r2 and then rs (connecting r1 and r2 in series). Result: Within the experimental errors, rs = r1 + r2. Therefore, the law of combination of resistances in series stands verified. Precautions: 1. The connections should be neat, tight and clean. 2. Plugs should be tightly connected in the resistance box. 3. The movement of the jockey should be gentle, and it shouldn’t be rubbed. 4. The null point should be between 40 cm and 60 cm. Sources of Error: 1. The screws of the instrument might be loose. 2. The wire might not be of uniform diameter. 3. Parallax error Circuit Diagram: Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 3 Observations table: Wires Sr. Resistance Length, Length 𝑫𝑪 = Unknown Mean No. R (Ohm) 𝑨𝑫 = (𝟏𝟎𝟎 − 𝒍) (cm) Resistance r(ohm) 𝒍(cm) 𝑹 (𝟏𝟎𝟎−𝒍) r= 𝒍 (ohm) 𝒓𝟏 1 2 3 𝒓𝟐 1 2 3 𝒓𝟏 𝐚𝐧𝐝 𝒓𝟐 1 𝐢𝐧 𝐬𝐞𝐫𝐢𝐞𝐬 2 𝒓𝒔 3 Calculations: Mean value of r1 = Mean value of r2 = Experimental value of rs = Theoretical value of rs = r1 + r2 = Difference = EXPERIMENT NO. 3 HALF DEFLECTION Aim: To determine resistance of a galvanometer by half-deflection method and to find its figure of merit. Apparatus: A Weston type galvanometer, battery eliminator, resistance boxes, two one-way keys, a rheostat, connecting wires and a piece of sand paper. 𝑅×𝑆 Theory: The resistance of the galvanometer is given by 𝐺 = where R is the resistance 𝑅−𝑆 and S is the shunt resistance. The figure of merit k of the galvanometer is given by Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 4  𝜀 𝑘 = (𝑅+𝐺) 𝜃 , where θ is the angle of deflection in the galvanometer. Procedure: Make the connections accordingly as shown in circuit diagram. See that all plugs of the resistance boxes are tight. Take out the high resistance (say 2000 Ω) from the resistance box R and insert the key K1 only. Adjust the value of R so that deflection is maximum, note the value of R and deflection θ. Insert the key K2 without changing the value of R. Adjust the value of S, such that deflection in the galvanometer reduces to exactly half the value of θ obtained. (i.e., θ/2). Note the value of resistance S. Repeat the steps three times taking out different values of R and adjusting S every time. Find the value of G using the 𝑅×𝑆 𝜀 formula, 𝐺 = 𝑅−𝑆. Also find the figure of merit k using the formula, 𝑘 = (𝑅+𝐺) 𝜃 Result: 1. Resistance of given galvanometer = …….. Ω 2. 3. Figure of merit of given galvanometer = A/div. Precautions: 1. All the connections should be neat, clean and tight. 2. All the plugs in resistance boxes should be tight. 3. The e.m.f. of cell or battery should be constant. 4. Initially a high resistance from the resistance box (R) should be introduced in the circuit (otherwise for small resistance an excessive current will flow through the galvanometer or ammeter can be damaged). Sources of error: 1. The screws of the instruments may be loose. 2. The plugs of resistance boxes may not be clean. 3. The e.m.f. of battery may not be constant. 4. The galvanometer divisions may not be of equal size. Circuit diagram: Observations: Emf of the battery, 𝜀 = 2 𝑉 Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 5  Serial Resistance Deflection Shunt Half Resistance of the Figure of merit No. in the G.M resistance deflection G.M R (ohm) 𝜀 𝑘= 𝜽 (𝒅𝒊𝒗. ) S (ohm) 𝜽 (div) 𝑅×𝑆 (𝑅 + 𝐺 ) 𝜃 𝟐 𝐺= (𝑜ℎ𝑚) 𝑅−𝑆 (A / div) 1 2 3 Calculations: 𝑅×𝑆 Resistance of the galvanometer, 𝐺 = 𝑅−𝑆 1. 2. 3. Mean value of G = 𝜀 Figure of merit, 𝑘 = (𝑅+𝐺) 𝜃 1. 2. 3. Mean value of k = EXPERIMENT NO. 4 A C SONOMETER Aim: To find the frequency of AC mains. Apparatus: A Sonometer, an electromagnet, step down transformer, slotted weights, clamp, stand, paper rider etc. Theory: When an alternating current (which is step down by a step-down transformer) is passed through an electromagnet, the iron core is temporarily magnetised twice in every cycle. As a result, the sonometer wire (made of magnetic material) is attracted towards the electromagnet twice in each cycle of AC. If the tension in the sonometer wire and its length Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 6 between the wedges is so adjusted that it is set into resonant vibration by AC, then the frequency of AC will be half than that of the frequency of vibration of the stretched string. 1 𝑇 1 𝑇 Frequency of vibration of stretched wire = 2𝑙 √𝜇 ∴ Frequency of AC, 𝜈 = 4𝑙 √𝜇 where l is the length of the sonometer wire in between the wedges at resonance. T- tension in the wire and µ - mass for unit length of the sonometer wire. Procedure: Place 1 kgwt on the hanger of the sonometer apparatus and switch on the AC supply. Place a paper rider on the sonometer wire and adjust the distance between the wedges so that the paper rider flies off. Measure the length (l1) of the wire in between the wedges. Do 𝑙 +𝑙 this once again to get the length (l2). Mean length, 𝑙 = 1 2 2 is calculated. Repeat the experiment by increasing the load in the hanger in steps of 1 kg. Result: - Frequency of AC mains = Precautions: 1. The wire should be made up of a magnetic material and should be free from kinks. 2. The pulley should be frictionless. 3. The lower end of the electromagnet should be held slightly above the sonometer wire and in the middle of the vibrating portion of the wire. Sources of error: 1. The sonometer wire may not have uniform cross-sectional area. 2. The pulley may not be frictionless. Hence, tension in the wire will be different from the load suspended. 3. The frequency of the AC mains may not be stable. Observation Table: Trial no. Load in the Tension Resonant length Frequency of AC hanger, M 1 𝑇 𝑙1 𝑙2 Mean 𝑙 𝜈= √ (kg) T=10M 4𝑙 𝜇 (N) (cm) (cm) (cm) (Hz) 1. 2. 3. 4. Mean frequency of AC = Calculations: Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 7  1 𝑇 Frequency of AC mains= 4𝑙 √𝜇. By substituting value of T = Mg = 10 M and µ = 5.1 x 10-3 1100√𝑀 kgm-1, we get a simplified formula. 𝜈 =. 𝑙 1. 2. 3. 4. Mean value of frequency = EXPERIMENT NO. 5 CONCAVE MIRROR Aim: - To find the value of v for different values of u in case of a concave mirror and hence find its focal length. Apparatus: - A concave mirror, mirror holder, illuminated wire gauze, white screen, metre scale. 𝟏 𝟏 𝟏 Theory: - The focal length, f of a concave mirror is given by the formula 𝒇 = 𝒗 + 𝒖 , where u- object distance, v - image distance. According to sign convention, 𝐮 is negative and 𝐯 is negative for a real image ∴ uv 𝐟 (= u+v ) is also negative. Procedure: - Find the rough focal length of the mirror by distant object method. Now place the object in front of the mirror at a distance greater than the rough focal length (about 1.5f). Measure this distance as u. Now place the screen in front of the mirror and adjust its position so as to get a clear image of the object and measure this distance as v. Repeat the experiment by changing the position of the object and measuring the image distance in each case. Result: - Focal length of the concave mirror = Precautions: 1. The distance should be measured accurately without parallax. 2. The object, the mirror and the screen should be vertical. 3. The mirror should be at the same height as the object. Sources of error: 1. Parallax error. 2. The object, the mirror and the screen may not be vertical. Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 8  3. Object and pole of the mirror may not be in the same level. Ray diagram: Observations: Rough focal length of the mirror = Trial No. Object distance Image distance Focal length (u) cm (v) cm uv 𝑓= (cm) u+v 1. 2. 3. 4. 5. Calculations: uv Focal length, 𝑓 = u+v (cm) 1. 2. 3. 4. 5. Mean focal length, f = EXPERIMENT NO. 6 CONVEX MIRROR Aim: To determine the focal length of the convex mirror using a convex lens. Apparatus: A convex mirror, convex lens, illuminated wire gauze, screen, scale etc. Theory: A convex mirror is placed between the lens and the screen in such a way that the image is obtained side by side with the object. This happens when the rays starting from the Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 9 object and refracted through the lens fall normally on the convex mirror. The distance PC 𝑅 gives the radius of curvature R of the mirror. Focal length, 𝑓 = 2. Procedure: Form and enlarged image of the wire gauze on the screen using a convex lens. The given convex mirror is introduced in between the lens and the screen with its reflecting surface towards the lens. The position of the mirror is adjusted to obtain the image of the wire gauze side by side with the wire gauze itself. Now the distance between the mirror and the 𝑅 screen is measured. This gives the radius of curvature R of the mirror. Focal length, 𝑓 = 2 is calculated. Repeat the experiment for different enlarged images of the object by the convex lens. Result: Focal length of the convex mirror = Precautions: 1. The object, lens, mirror and the screen should be vertical. 2. The convex lens should be of short focal length. 3. The distances should be measured without parallax. Sources of error: 1. Parallax error. 2. The object, mirror and lens may not be at the same height. 3. Focal length of the convex lens may be large. Ray Diagram: Observation table: Trial No. Distance between the screen and 𝑹 Focal length, 𝒇 = 𝟐 (cm) the mirror, R (cm) 1. 2. 3. 4. 5. Mean focal length, f = EXPERIMENT NO.7 CONVEX LENS Aim: - To find the focal length of a convex lens by plotting graphs between u and v. Apparatus: - A convex lens, lens holder, illuminated wire gauze, screen, metre scale. Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 10 Theory: - The focal length, f of a convex lens is given by 1 1 1 the formula 𝑓 = 𝑣 − 𝑢 , where u- object distance, v - image distance. According to sign convention, u is negative. 1 1 1 𝑢𝑣 ∴ = + 𝑜𝑟 𝑓 = 𝑓 𝑣 𝑢 𝑢+𝑣 𝑶𝑨+𝑶𝑩 From u – v graph, 𝒇 = 𝟒 Procedure: - Find the rough focal length of the convex lens using distant object method. Mount the lens in the lens holder and place it so that the illuminated wire gauze (object) and screen are on its either side. Keep the object at twice the focal length (rough) of the convex lens. Adjust the distance of the screen till a real, inverted image of the object is formed on the screen. Note the distance between object and lens (u) and also the distance between image (screen) and lens (v). Repeat the experiment by changing the object distance by a few centimetres and the corresponding values of image distance are measured without parallax error. A graph is drawn taking u along negative X axis and v along positive y axis. (Same scale and same origin should be chosen for both axes). The bisector of the angle is drawn meeting the curve at C. CA is drawn parallel to y axis meeting the X axis at A. Similarly, CB is drawn parallel to X axis meeting the y axis at B. OA and OB are determined. Result: - Focal length of the convex lens from the graph = cm = m. Precautions 4. The distance should be measured accurately without parallax. 5. The object, the lens and the screen should be vertical. 6. The tip of the needles should be at the same height as the optic centre of the lens. Sources of error 4. Parallax removal may not be perfect. 5. The object, the lens and the screen may not be vertical. 6. The object, lens and the image may not be in the same line. Ray Diagram Observation table: Trial Object distance (u) cm Image distance (v) cm 1. 2. 3. Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 11  4. 5. 6. Calculations From graph OA = cm OB = cm 𝑂𝐴+𝑂𝐵 𝑓= = 𝑐𝑚 = 𝑚. 4 EXPERIMENT NO.8 CONCAVE LENS Aim: - To determine the focal length of a concave lens using a convex lens in contact. Apparatus: - convex lens, concave lens, illuminated wire gauze, screen, lens holders, scale etc. 𝒖𝒗 Theory: - According to lens equation, focal length of a lens, 𝒇 = 𝒖+𝒗 When a convex lens of focal length f1 is placed in contact with a concave lens of focal 1 1 1 1 1 1 length f2, the focal length F of the combination is given by 𝐹 = 𝑓 + 𝑓 𝑜𝑟 𝑓 = 𝐹 − 𝑓 1 2 2 1 1𝐹𝑓 𝑖. 𝑒. 𝑓2 = 𝑓 −𝐹 ∙ (f2 will be negative). 1 Procedure: - An illuminated wire gauze is placed on one side of the convex lens and a screen is placed on the other side. The position of the screen is adjusted to obtain a clear image of the object on it. The distance of the object from the lens (u) and the distance of the image from the lens (v) are measured. Calculate the focal length f1 of the convex lens 𝑢𝑣 using the formula. 𝑓1 = 𝑢+𝑣 ∙ Repeat the experiment and find the mean value of focal length 𝑓1. Now the given concave lens is kept in contact with the convex lens and the focal length F of the combination is also determined by u – v method. 1 𝐹𝑓 Calculate 𝑓2 using the formula, 𝑓2 = 𝑓 −𝐹 1 Result: - Focal length of the concave lens = cm = m. Precautions: - 1. The convex lens must be of shorter focal length than the concave lens. 2. The distance should be measured accurately without parallax. Sources of error: - 1. Parallax error. 2. The lenses may not be at the same height as that of the object. Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 12 Ray diagram: - Observation table: - 𝒖𝒗 Lens used Trial Distance of Distance of image 𝒇= Mean focal 𝒖+𝒗 No. object from from lens (v) cm (cm) length (cm) lens (u) cm Convex 1. Lens (f1) 2. f1 = 3. Combination of 1 Convex and Concave 2. F= Lens (F) 3. Calculations: - Mean value of f1 = cm, Mean value of F = cm 𝐹×𝑓1 Focal length of the concave lens, 𝑓2 = = 𝑓1−𝐹 *************************************************************************** ACTIVITY – A (1) Aim: - To assemble the components of a given electrical circuit (ohm's law circuit). Apparatus: - An unknown resistance, a battery, voltmeter and an ammeter of appropriate range, a rheostat, one way key, connecting wires etc. Theory: - When a potential difference V is applied across a resistor R, the current is given 𝑉 by 𝐼 = 𝑅. (Ohm’s law) Procedure: - The connections are made as shown in the figure. The least counts of the voltmeter and ammeter are recorded. A suitable current is passed through the circuit by adjusting the rheostat. The voltmeter reading V and the current I through the resistor is noted. The resistance of the given wire R is 𝑉 calculated using the formula by 𝑅 =. The 𝐼 Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 13 experiment is repeated for different values of potential difference by adjusting the rheostat. Observations: - Least count of the voltmeter = Least count of the ammeter = Trial No. Voltmeter reading Ammeter reading Resistance V (volt) I (A) 𝑉 𝑅=𝐼Ω 1 2 3 Conclusion: - The components are connected and the value of resistance R is calculated. ACTIVITY – A (2) Aim: - To draw the diagram of a given open circuit consisting of at least a battery, resistor, rheostat, key, ammeter and voltmeter. Point out the components that are not connected in proper order and correct the circuit. Draw the corrected circuit diagram. Apparatus: - A battery, a resistor, an ammeter, voltmeter, rheostat, one way key and connecting wires. Theory: - Voltmeter is a higher resistance instrument and it should be connected in parallel across a resistor to measure the potential difference across it. If it is connected in series as in figure 1, practically no current will flow through the circuit. An ammeter is a low resistance device and it should be connected in series to measure the current through a circuit. If it is connected as in figure 1, almost the whole current will pass through the ammeter and the resistor R will be by passed. A rheostat is used in the circuit for varying the current. If it is connected as in figure 1, the resistance of the rheostat and hence the current will be constant. Procedure: - Mark the components that are not connected in proper order in figure 1. Draw the corrected circuit diagram (figure 2) and connect the components as in this diagram. Close the key, slide the rheostat contact and see that the ammeter and voltmeter readings are vary properly. Corrections: - Voltmeter is connected in parallel with the resistor. Ammeter is connected in series. One base terminal and the top terminal of the rheostat are connected. Conclusions: - The components which are not connected in proper order in the given circuit is marked. The circuit is corrected and the circuit diagram is drawn. Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 14  ACTIVITY – A (3) POTENTIAL GRADIENT ALONG A WIRE Aim: - To study the variation of potential drop with the length of a wire for a study current and hence find the potential gradient along the wire. Apparatus: - The given uniform wire, voltmeter, battery, rheostat, key, jockey, connection wires etc. Theory: - When a study current is passed through a wire of uniform cross section, the potential drop between two points on the wire is directly proportional to the length of the wire 𝑉 𝑉 between the points. That is, potential drop 𝑉 ∝ 𝑙, 𝑜𝑟 𝑙 = 𝑘, a constant. This ratio 𝑙 is called the potential gradient. It is a constant for a uniform wire carrying a constant current. Procedure: - The connections are made are shown in figure. The positive terminals of the battery and voltmeter are connected to the terminal A of the wire. The negative terminal of voltmeter is connected to the jockey J. The jockey is pressed at a distance (say 40 cm) from A. The rheostat is adjusted so that the voltmeter shows a suitable reading. There after the current in the wire is kept constant. So, the rheostat should not be adjusted again. The jockey is then pressed at a distance 80 cm, 120 cm,160 cm…. from A and the corresponding voltmeter readings are noted. The potential gradient is calculated in each case. Observations: - Least count of the voltmeter = Trial No. Length of the wire Voltmeter reading V Potential gradient from A (cm) (volt) 𝑉 (volt / cm) 𝑙 1 2 3 4 5 ACTIVITY – B (1) Light dependent resistor (LDR) Aim: - To study the effect of light (by varying the distance of the source) on an LDR. Apparatus: - LDR, light source, multimeter etc Theory: - A light dependent resistor is prepared from a semiconducting material cadmium sulphide. The resistance of a semiconductor decreases as the number of charge carriers increases. As the intensity of light incident on an LDR increases, the number of charge carriers in it increases and hence the resistance decreases. Intensity of light from a source Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 15 decrease with distance from it. Thus, the resistance of LDR increases as the distance from the light source increases. Procedure: - The LDR is placed at a distance of 40 cm from a source of light. It is exposed to light for about one minute. The resistance of LDR is measured by using a multimeter. The experiment is repeated by increasing the distance of LDR from the source. Observations: - Sr.No. Distance of LDR from the Resistance source. (cm) (kΩ) 1 2 3 4 5 Result: - The resistance of LDR increases as its distance from the source of light increases. ACTIVITY – B (2) Aim: - To identify a diode, an LED, a resistor and a capacitor from a mixed collection of such items Theory: - Diode is a 2-terminal device which conducts only when it is forward biased and does not conduct when it is reversed biased. LED (light emitting diode) is a special type of junction diode having 2 terminals. The LED conducts when it is forward biased and does not conduct when it is reversed biased. LEDs are of different colours like red, green, white etc Resistor is a 2-terminal device used to control the current flow by offering the opposition in its path Capacitor is a 2-terminal device which does not conduct but stores some charge when DC voltage is applied. Procedure: - Pick a component from the given mixed collection of items. It could be a resistor, a capacitor, a diode or an LED. Look for the component having colour bands or 3 sets of colours followed by a silver or gold bar. This component is a resistor. One can verify the component by using multimeter only. Ensure that the multimeter is set up in the resistance mode of highest range. Connect or touch the multimeter terminals to the component terminals and watch for multimeter deflection. Also repeat it by reversing the component terminals. In both cases, if equal deflection is shown in the multimeter scale then the component is a resistor. If on connecting the terminals, the large the deflection in the multimeter scale is observed which gradually returns to zero, then the component is a capacitor of large value of capacitance. If a capacitor having small value of capacitance is given, then there is no deflection in the multimeter scale rather the point remains at 0 position. If the multimeter shows some deflection in one direction with the emission of light from the component and much less or 0 deflection in the other direction (or an unequal deflection with the emission of light), then the component is an LED. Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 16  If the multimeter shows some deflection in one direction but with no emission of light from the component and much less or 0 deflection in other direction, then the component is a diode. Result: - A diode, an LED, a resistor and a capacitor are identified one by one from a given mixed collection of such items. Observations: - Sr.No. State of conduction Emission of light Name of the device 1 Conducts in one direction only No Diode 2 Conducts in one direction only Yes LED 3 Conducts in both directions No Resistor 4 Does not conduct, gives an initial No Capacitor deflection which decays to zero. ACTIVITY – B (3) Aim: - To study the nature and size of the image formed by a convex lens using a candle and a screen. Apparatus: - The given convex lens, screen, candle, match box, scale etc. Theory: - The position, nature and relative size of the image of an object formed by a convex lens depends on the position of the object with respect to the lens. Procedure: - The approximate focal length of the given convex lens is determined first by obtaining a sharp and well-defined image of a distant object on the screen. The distance between the lens and the screen gives the focal length of the lens. The convex lens is mounted on a stand. A straight line is drawn on the horizontal table. The convex lens mounted on the stand is placed at the centre of the line. The distance F and 2F from the lens are marked on either side of the lens. The lighted candle fixed on a wooden block is placed far away from2F on one side. The screen is placed on the other side of the lens on the line. The centres of the flame, lens and the screen must lie on a horizontal level. The screen is slowly moved along the line until a sharp and well-defined image is obtained on it. The position and nature of the image are noted. Similarly, the position size and nature of the image of the candle flame are recorded by keeping the candlelight at 2F, between F and 2F, at F and between F and the optic centre. When the object is at F, it is found that, at no position of the screen a sharp and well-defined image is formed on it, only a general illumination is seen. This shows that the image is actually at infinity in this case. Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 17  When the object is in between the focus and the optic centre, no image is obtained on the screen. But an enlarged, erect image is seen through the lens. The image is virtual. The observations are recorded. Result: - The position, nature and size of the image formed by a convex lens for different positions of the object is studied. Observations: - Approximate focal length of the lens = Position of the Sr. No. Object Image Nature of the Size of the image image 1 At infinity At F Real, inverted Highly diminished 2 Beyond 2F Between 2F and F Real, inverted Diminished 3 At 2F At 2F Real, inverted Same size 4 Between 2F Beyond 2F Real, inverted Magnified and F 5 At F At infinity Real, inverted Highly magnified 6 Within F Beyond F Virtual, erect Magnified Ray Diagrams: - 1. Object at infinity 2. Object beyond 2F Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 18 3. Object at 2F 4. Object between F and 2F 5. Object at F 6. Object between F and C *************************************************************************** Susamma Shajan/ ST. THOMAS CENTRAL SCHOOL 19