mm EXPERIMENT 1 Mt AIM: To find the value of v for different values of u in case of a concave mirror and to fing yy, focal length. APPARATUS An optical bench with three uprights (zero end upright fixed, two outer uprights with lateray movement), concave mirror, a mirror holder, two optical needles (one thin, one thick), a knitting Needle and a half metre scale. THEORY From mirror formula, e of the mirror. V have negative values. Hence, f comes negative.ength of Spherical Mirrors focal Length of 429 pROCEDURE ‘qo determine rough focal length 1, Mount the concave mirror in mirror holder. 2, Go out in the open and face the mirror towards distant tree or building. Obtain the image of the tree or the building on a white ilding on a white painted wall (screen) and move the ritror forward and backward to get a sharp image on the wall. Measure the distance between the 1d the wall (screen). This will be ‘mirror and the wall (screen). This willbe equal tothe rou focal length of the mirror. 7” {Wote, Similar procedure is adopted for determining rough focal length of a convex lens.) Toset the mirror 5. Place fixed upright near zero end of the optical bench and the two other uprights (with lateral movement) near the other end. 6, Clamp the holder with mirrorin the fixed upright keeping mirror face towards other end of the bench and surface perpendicular to its length. 7. Make mirror surface vertical using levelling screws of the optical bench. (In final adjustment, the principal axis of the mirror must be horizontal and parallel to the optical bench). 8. Note the position of the index mark on the base of mirror upright. To set the object needle 9, Take the thin optical needle as object needle (0). Mount it in second upright. 10. Move the object needle upright and clamp it at a distance (in full cm) nearly 1.5 times the obtained rough focal length of the mirror. 11, Adjust height of the object needle to make its tip lie on horizontal line through the pole of the mirror. 12. With left eye closed, see with the right open eye from the other end of the optical bench. An inverted and enlarged image of the needle will be seen Tip of the image must lie in the middle of the mirror (If image is not seen, move object needle upright away from the mirror). 15. Note the position of the index mark on the base of the object needle upright. in third upright and move the upright near the its tip is seen in line with the tip of the image The image tip and the image needle 7.08 (#)]. The parallax gets removedTo determine index correction rection for distance between pote of mirror and tip ofthe object needle and role of mirror and tip of the image needle as described. [Section 7.10 (2 "ef | ‘ror in steps of 1.cm to get observation 2 and 1. Re nea | 20, ind index co distance between P Move object needle upright towards mi the experiment. from mirror (from position of observation 2) in steps PSO Ley 22, Move object needle upright away’ to get observations 4, Sand 6. Repeat the experiment. 3. Record all the observations as given ahead. [Note Order of observations, sept, 3,2, 1,4, 5 and G to eneure that object always ies betwe en dita and 2f even when found rough focal length may be too rough) OBSERVATIONS ‘Rough focal length of the given concave mirror ‘Actual length of the knitting needle, x Observed distance between the mirror and object needle when (am) (am) | fw along X-axis and vt are negative. Plot tion table. The otTP paawaline OA making an angl i brawling OAmaRinga ange o 45 whether axe, 9 geo a point A: Draw AB and AD perpendicular on X'- and Yuages ene OX aed meeting the core Tame fr point A. So the coordinates Of pln nt 880 Fespectvey, The values of w and ore nly when the object i placa a et 220 beau ors conve ion s at the centr Hence, wavs Rea pees rom mirror formula applied to point A wi vow 2 u v i uated or 5 and fe$ or £ Hence, half the values of either coordinate of A (ie, distance OD or OB) gives the focal length «ofthe concave mirror, ,132 eee ——— Ay elect a suitable but the same scale fOFEPFEHDE ONG X-y, ot ean eet et poeta nn be i i pct oats of an mth trevaen ben da enh ames cut tbe tight ine at town Fe % rapn eerween? aNot bond X-axis : 1.6m ; Y- ene eee : ints A and B, respectiveall” s, intercept OB ae 133 Pn 1 = 0, then qnus, intercept OA a) RESULT ‘The focal length of the given concave mirror as determined from: ey wv ) focal length calculated from f = ee Ca Gi) (u-v) graph & 2 graph Gv) (u-v) graph PRECAUTIONS Principal axis of the mirror should be horizontal and parallel to the central line of the optical bench. ‘The uprights should be vertical. Tip to tip parallax should be removed between the needle I and image of the needle 0. To locate the position of the image the eye should be at least 30 cm away from the needle _ Tips of the object and image needles should lie at the same height as that of pole of the concave mirror. 6. Index correction for u and v should be applied. 2. ae 4 5. SOURCES OF ERROR 1. ‘The uprights may not be the vertical. 2. Parallax removal may not be perfect.jm sCEXPERIMENT 3 = i a of a convex lens by plotting graphs between u and v or between ee appARATUS ‘hn optical bench with three uprights (central upright fixed, two outer uprights with lateral ovement), a convex lens with lens holder, two optical needles, (one thin, one thick) a knitting needle aha metre scale rg THEORY ‘The relation between u, v and ffor a convex lens is, Leia, eee Sp. few fw uo vere, f=focallength of convexlens u= distance of object needle from optical centre ofthe lens v= distance of image needle from optical centre of the lens.by Comprehensive Practc v j 150 al Phy ‘and the wall (screen). This wil be qua ey, 4 4, Measure the distance between the mirror focal length ofthe mirror. mm ro sot the lens va ight and keep the upright at 50 cm mark 5, Clamp the holder with lens in a fixed upri i ha that ite surface is vertical and perpendicular to the length ofthe, ta Adjust the lens sul bench 2. Keep the upright fixed inthis position throughout. Toset the object needle 6, Take the thin optical needle as object needle (0). Mount it in outer laterally moveable pe, near zero end. 8. Move the object needle upright and clamp it at a distance (in full cm) nearly 1.5 times 4. ‘obtained rough focal length of the lens. 410. Adjust height of the object needle to make its tip lie on horizontal line through the optcj centre ofthe lens, a 11, Note the position of the indes To set the image needle 12, With eft eye dosed, see rk on the base of the object needle upright. ‘eye from the other end of the optical bench. ln dle will be seen. Tip of the image rmust lien theyvength of Sphenica’ Lenses el , s6nVATIONS i ough focal length of the given convex lens ‘Actual length of the knitting needle cen observed distance between the object needle andtheleng when knitting needle is placed between them . Observed distance between the imageneedleandthe lens when knitting needle is placed between them Index correction for the object distance u, Index correction for the image distance v, pe apa CALCULATIONS () wv Graph, Selec a suitable but the same scale to represent «along X-axis and v along Y-axis, ‘According to sign conventions, inthis case, us negative and vis positive. Plot the various points for different sets of values of uand v from observation table second quadrant. The graph comes, ‘out to be a rectangular hyperbola as shown in graph between u and v. Draw aline OA making an angle of 45° with either axis (i. bisecting ZYOX’) and meeting the curve at point A. Draw AB and AC perpendicular on X'- and Y-axes, respectively ‘The values of u and v will be same for point A. So, the coordinates of point A must be (2f,2f), ‘because for a convex lens, when u = 2f, v= 2f. na AB=AC=2f or OC=OB=2f i fo Band f=.Comprehensive Practical Physi my 152 GRAPH BETWEEN u AND v Scale X-axis: 1 om =... om of U IM Y-axis: 1.0m = 1.6m OF 3 a rectangular hyperbola. , 1 to) = sand + torepresent 7 along X-axis and jan, - Plot the various points for different ‘comes out to be a straight int * at points Pand Q, respectivy OP and OQ.ivength of Spherical Lenses roca GRAPH BETWEEN 1 anp t Seale puny Xtaxis | 1m = .,.... emt ott Y-axis : 4 om =... ome of 1 i fii 153RESULT The focal length of the given convex lens as determined from: 1. focal length, f 2. (u-v) graph =.. ier 3.4 -2}eranh= ig cm and 4. (u-v) graph =......cm. PRECAUTIONS 1. Tips of the object and image needles should lie at the same height as the centre of the lens 2. Parallax should be removed from tip to tip by keeping eye at a distance at least 30 cm away from the needle. 3. The object needle should be placed at such a distance that only real, inverted image of itis formed. 4, Index correction for u and v should be applied.SOURCES OF ERROR 1. The uprights may not be the vertical. 2. Parallax removal may not be perfect.eos 165 = EXPERIMENT 5 = ppARATUS Drawing board, a white shee jh paper and a protractor. ea ‘THEORY The refractive index (n) of the material ofthe AsD, sin ( re aR iz where, D,, is angle of minimum deviation and Ais angle of the prism, of Paper prism, drawing pins, pencil halt metre sale, offce pins, prism is given by, Ip of drawing pins or tape, ly in the middle of the paper.Comprctensive Practical Physics yy oon the straight line XX’ at suitable distances of about 5 cm. as shown in diagrarn 60° (write value of the 166 3, Mark points Q,, Qy, Qy- 4. Draw normals N,Q, N,Q, N,Q,, on points Q,, QQ, 5. Draw straight lines R,Q,, R,Q,, R,Q,, .. making angles of 35", 40°, angles on the paper) respectively with the normals, Mark one corner of the prism as A and take it as the edge of the prism for all the observations 7. Puta prism with its refracting face AB in the line XX’ and point Q, in the middle of AB, SS. Mark the boundary of the prism. 9. Fix two or more office pin P, and P, vertically on the line R,Q,. The distance between the ping should be 10 mm or more. 10. Look the images of point P, and P, through face AC. 11. Close your left eye and bring open right eye in line with the two images. 12. Fix two office pins P, and P, vertically, and 10 cm apart such that the open right eye sees ping and P, and images of P, and P, in one straight line. 25. Remove pins P, and P, and encircle their pricks on the paper. 4 eT fori =40°,.., 60°. To measure D in different cases SNE. and P, (pin pricks) to obtain emergent rays S, “eee dex ofPrsm Mater, Glass Sib and Transparent Lg {LATIONS cate Fate Fe ane tet tnd ang of deat 2 by ing ong he 2 on na EMP Gnd veo spon corresponding ot rat pol ofthe rah RROBABLE GRAPH BETWEEN 2) AND Scale of deviation (D) frst Bee occas nange168 Comprehensive Practical Phys PRECAUTIONS 1. The angle of incidence should lie between 35°-60°. 2. The pins should be fixed vertical. 3. The distance between the two pins should not be less than 10 mm. 4. Arrow heads should be marked to represent the incident and emergent rays. 5. The same angle of prism should be used for all the observations. SOURCES OF ERROR 1. Pin pricks may be thick. 2. Measurement of angles may be wrong.y me EXPERIMENTS i AIM: To draw the I-V characteristic curve of a p-n junction in forward bias and reverse bias, APPARATUS A pn junction (semi-conductor) diode, a 3 volt battery, a 50 volt battery, a high resistance theostat, one 0-3 volt voltmeter, one 0-50 volt voltmeter, one 0-100 mA ammeter, one 0-100 HA ammeter, one way key, connecting wires and pieces of sand paper. THEORY Fe - When the p-section of the diode is connected to positive terminal of a battery ary n-section is connected to negative terminal of the battery then junction is said to be forward biased. With increase in bias voltage, the forward current increases slowly in the beginning and then rapidly. At about 0.7 V for Si diode (0.2 V for Ge), the current increases suddenly ‘The value of forward bias voltage, at which the forward current increases rapidly, is called cut in voltage or threshold voltage. Reverse- s. When the p-section of the diode is connected to negative terminal of high voltage batten of the diode is connected to positive terminal of the same battery, then junction is said to be reverse biased. When reverse bias voltage increases, initially there is a very small reverse current flow, which remains almost constant with bias. But when reverse bias voltage increases to sufficiently high value, the reverse current suddenly increases to a large value. This voltage at which breakdown of junction diode occurs (suddenly large current flow) is called zener breakdown voltage or inverse voltage. The breakdown voltage may starts from one volt to several hundred volts, depending upon dopant density and the depletion layer.poe Potential Divider Fig. p-n junction diode—reverse biased. ‘Make circuit diagram as shown in diagram. Make all connections neat, clean and tight. ». Note least count and zero error of voltmeter (V) and milli ammeter (mA). | Bring moving contact of potential divider (rheostat) near negative end andinsert the key K. Voltmeter (V) and milli-ammeter (mA) will give zero reading. . p ds positive end to apply a forward-bias voltage (V,) of suddenly. This represents “forward breakdown” stage. —186 Comprehensive Practical Physics xy 12. Make circuit diagram as shown in diagram. 13, Make all connections neat, clean and tight. 4. Note least count and zero error of voltmeter (V) and micro-ammeter (iA). 15, Bring moving contact of potential divider (theostat) near positive end and insert the key K. Voltmeter (V) and micro-ammeter (A) wil give zero reading. 15. Move the contact towards negative end to apply reverse-bias voltage (V, of 0.5, afeebly reverse current starts flowing, 17. Increase V, in steps of 0.2 V. Current increases first slowly and then rapidly till V, becomes 20V. Note the current: . 1S. Make V, = 25 V. The current increases suddenly. This represents “reverse breakdown’? stage. Note the current and take out the key at once. 19. Record your observations as given ahead. OBSERVATIONS, For forward-bias 0 ° ° ° os a A 3 s 78 a0 as 20ower and Transistors 187 yor of voltmeter it of voltmeter tine yesstcourt se error of voltmeter ana cof micro-ammeter past count of micro-ammeter ine WA ero error of micro-ammeter », Table forCompretansive Practical Physcs— 188 ic curve of a junction diode. ‘This graphis called forward-bias characteris FORWARO-BIAS CHARACTERISTIC CURVE OF & JUNCTION DIODE Scale Xaaxis tem =0.2Vot Vp ye Yeaxis : 1 om = 5 MA of le ka 4s 40 A= 10mA current [, (column)189 ‘las characteristic Curve of ' CURVE OF A JUNGTION DIODE Kad tom= ovary Yeas: tom= Su acy istic curve ofa junction diode (reverse-bias) 2 a i point AtoB, eet SOW =2V, 8, = (2-D)uA= ua 4 reverse-bias, 2 2V anit Fe ace wd. ‘oa not be applied. not be applied