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DELTA UNIVERSITY FOR SCIENCE AND TECHNOLOGY FACULTY OF ORAL AND DENTAL MEDICINE HANDOUT FOR PRACTICAL PHYSICS II LAB SPRING 2016 Prepared by physics group, All rights are reserved to the Faculty of Oral and Dental Medicine, Delta University for Science and Technology. 1 Contents Experiment No. (01) Power of Spherical Lenses ---------------------------------------------------------------- 3 1. Determination of the Focal Length and the Power of a Converging (Convex) Lens ------------------------- 3 1.1. Coincidence Method: -------------------------------------------------------------------------------------------- 3 1.2. General Method: ------------------------------------------------------------------------------------------------- 4 2. Determination of the Focal Length and the Power of a Diverging (Concave) Lens ------------------------- 5 Experiment No. (02) Determination of the Refractive Index of a Liquid using Liquid Lenses ------------- 7 1. Using concave mirror ------------------------------------------------------------------------------------------------ 7 2. Using Convex Lens and Plane Mirror ------------------------------------------------------------------------------ 8 Experiment No. (03) Power of Spherical Mirrors ------------------------------------------------------------- 10 1.Determination of the power and the focal length of concave mirror: 10 1.1. Coincidence Method: ------------------------------------------------------------------------------------------- 10 1.2. General Method: ------------------------------------------------------------------------------------------------ 10 2. Determination of the power and the focal length of Convex mirror: --------------------------------------- 12 Group Method: ------------------------------------------------------------------------------------------------------- 12 Experiment No. (04) The Prism --------------------------------------------------------------------------------- 13 Experiment No. (05) Verification of ohm's law by tangent galvanometer ---------------------------------- 15 Experiment No. (06) Comparison between the Magnetic Moments of Two Magnets using the Deflection Magnetometer ---------------------------------------------------------------------------------------------------- 18 2 Experiment No. (01) Power of Spherical Lenses 1. Determination of the Focal Length and the Power of a Converging (Convex) Lens 1.1. Coincidence Method: Fig (1.1): The focal length of a convex lens using coincidence method Method 1. Keep a light source (O) (illuminated arrow) at a distance from the lens and keep a plane mirror behind the lens such that the mirror surface is perpendicular to the lens axis. 2. Adjust the position of the lens until a sharp image (I) is formed on the surface contains the source (O). 3. Record the distance between the lens and the light source (O). This distance measures the focal length (f) of the lens. 4. Repeat the steps (2 and 3) many times and calculate the average value of the distances, which must be nearly equal. Results No. 1 2 3 Average f( ) Main value of the focal length of the lens ( f ) = Power of the lens F 100 100 f 3 1.2. General Method: Fig (1.2): The general form of lens position Method 1. Put the lens on its holder and keep the distance of an illuminated arrow (O) from the lens greater than the approximate focal length of the lens. 2. Looking from the other side of the lens adjust the position of a screen until a sharp image of the used arrow (I) is formed on the screen. 3. Record the readings on the optical bench meter scale corresponding to the positions of (O) and (I) from the lens, (x) and (y), respectively 4. Repeat for different observations (not less than five). 5. Complete the table and find F=(X+Y). Results No. x y X( ) Y( ) F=X+Y 1 2 3 4 5 Average power of convex lens (Fav) = 4 2. Determination of the Focal Length and the Power of a Diverging (Concave) Lens fg Fig (2.1): The group method for concave (diverging) lens Method 1. Put the converging lens in contact with the diverging lens on a holder in front of the source of light (O) in such away that the convex lens is facing the light source. 2. Put a plane mirror on a holder behind the group of lenses. Move the holder of the two lenses until a sharp image is formed on the source surface, as in Fig (2.1). 3. Measure the distance between the source and the middle of the holder of the lenses. This distance equals the focal length of the group of lenses (fg). 4. Repeat these steps many times. Calculate the average of the group focal length. 5. Calculate the power of the group (Fg). 6. Find the focal length of the converging (convex) lens by any method say it is (f1 cm). Then calculate its power (F1). 7. Determine the power of the diverging lens (F2). Results No. fg ( 1 2 3 Average ) Mean value of the group focal length ( fg ) = Power of the group of lenses Fg 100 100 fg 5 Focal length of the converging lens (f1) = Power of the converging lens F1 100 100 f1 Power of diverging lens ( F2 ) = Fg - F1 = Focal length of diverging lens f 2 100 100 F2 6 Experiment No. (02) Determination of the Refractive Index of a Liquid using Liquid Lenses 1. Using concave mirror Method 1. Place the concave mirror horizontally on the wooden block. 2. With the help of the optical needle, remove the parallax between the needle and its image. This position of the tip of the needle corresponds to the centre of curvature of the mirror. Measure the distance (PC = r). 3. Now pour a little quantity of the liquid on the mirror and again remove the parallax between the needle and its image. Measure the distance (PC' = r'). 4. Repeat the observations many times. Results No. PC = r ( ) PC' = r' ( ) n = PC/PC' = r/r' 1 2 3 Average Refractive index of the liquid (n) = 7 2. Using Convex Lens and Plane Mirror Method 1. Place a plane mirror on the stand and a convex lens over it. 2. Put a solid arrow in the clamp of the stand and move it till an inverted image is formed. Now remove the parallax between the arrow and its image. 3. Measure the average of the distance of the arrow from the plane mirror and from the upper surface of the lens. This gives the focal length of the convex lens (f). 4. Repeat this several times and find out the mean value of (f). 5. Now place a few drops of the given liquid in between the lens and the mirror. So that, a thin plane-concave lens of the liquid is formed. 6. Now adjust the arrow along the vertical stand till its inverted image formed by the combination coincides with the arrow i.e., when no parallax exists 7. Measure the average of the distance of the arrow from the plane mirror and from the upper surface of the lens, which is the focal length (fg) of the combination. 8. Repeat the three steps many times and find out the mean value of (fg). 9. Calculate the refractive index (n). 8 Results No. f ( ) fg ( ) 1 2 3 Average Mean of focal length of convex lens (f) = Mean of focal length of group lens (fg) = The power of the liquid lens (FL) = FL 100 100 100 100 fg f The refractive index of the liquid (n) = R n 1 FL 1 100 100 9 Experiment No. (03) Power of Spherical Mirrors 1. Determination of the power and the focal length of concave mirror: 1.1. Coincidence Method: Method: 1. Put the mirror in front of the source and move it until you get sharp image. 2. Measure the distance from the mirror to the illuminated object, which is the radius of curvature (r). 3. Repeat the Last steps many times and take the average of (r). Results: No. 1 2 3 Average R Mean value of the radius (r) = … Cm Focal length (f = r / 2) = ….. Cm Power of the mirror (F) = …… Diopter 1.2. General Method: 10 Method: 1. Put the mirror at a distance greater than its focal length. then move a screen between the mirror and the illuminated object until you get sharp image. 2. Record the distance from the illuminated object to the mirror is (x) and the distance from the screen to the mirror is (y). then calculate X, Y and F=X+Y 3. Repeat the above steps for different values of (x) 4. Plot a relation between X, Y and then calculate the power from the intersections of the straight line. Results: Observation x y X Y F=X+Y 1 2 3 4 5 Average power from the table (Fav) = … Diopter 11 2. Determination of the power and the focal length of Convex mirror: Group Method: Determination of the Group radius Determination of the lens' power Method: 1. Find the focal length (fL) of the convex lens by any method. then calculate the power of the convex lens FL = 100 / fL 2. Place the convex lens with the convex mirror on the same holder, and move the group until you get sharp image. 3. Record the distance from the group to the illuminated object as (rg). 4. from (rg) calculate the focal length of the group (fg) then Fg = 100 / fg 5. Calculate the power of the convex mirror by F m = Fg – 2·FL which is a negative value. Results: Observation 1 2 3 Average rg Mean value for (rg) = … Cm Focal length of the group (fg) = rg / 2 Power of the group (Fg = 100 / fg) = … Diopter Focal length of the convex lens (fL) = … Cm Power of the convex lens (FL) = 100/fL = …. Diopter Power of the convex mirror (Fm) = Fg – 2·FL = … Diopter 12 Experiment No. (04) The Prism Method: [A] Determination of the apex angle(A): 1. Put the prism with its triangular base on the paper and draw the prism. 2. Draw two parallel lines with the apex in the center of the distance between them as in the figure. 3. Put two pins on the line ED and look in the same face to find the reflected image of the pins. then put another two pins inline with the images of the pins. 4. Remove the pins and draw a line connecting the positions of the pins to obtain the direction of the reflected ray. 5. Repeat the same on the other face of the prism. 6. The angle between the two reflected rays is (2A) from which we determine the Apex angle (A). [B] Determination of the minimum deviation angle (δmin): 1. Put the prism on its triangular face and draw it on the paper. 2. Draw HD to represent the incidence ray with incidence angle (i) with the normal to the face. 3. Put two pins on the Line HD and look for the image of the two pins in the opposite face, then put another two pins inline with the pins images. 4. Draw EF by connecting the positions of the two pins to represent the refracted beam. 5. Record the angle of deviation which is the angle between the incidence and refracted beam. 6. Repeat all the steps with different incidence angles to obtain the corresponding deviation angle. 7. Draw a relation between the incidence and deviation angles and determine the minimum deviation angle δmin from the graph as shown in the figure 8. by Using the value of the Apex angle (A) and (δmin) calculate the refractive index (n) from the relation 13 A min Sin 2 n A Sin 2 Results: Incidence Angle 35 40 45 50 55 Deviation Angle A= δmin = n= 14 Experiment No. (05) Verification of ohm's law by tangent galvanometer Theory: Ohm's Law: "Voltage is directly proportional to the current for constant temperature." For the tangent Galvanometer: The magnetic field (H) formed due to a current ( I ) passing in the coil is given by: H 2NI 10r The pointer deflects by angle (θ), which is because of two perpendicular fields: 1) The magnetic field produced by the coil (H). 2) The horizontal component of earth's magnetic field (Ho). And the relation is given by: H=Ho · Tan(θ) H Ho Tan( ) 2NI Ho Tan( ) 10r 10rHo I Tan( ) 2N I K Tan( ) where K 10rHo 2N Using Ohm's law for this circuit which has the form: I V R Ro Substitute in the above equation: V K Tan( ) R Ro or Cot ( ) K ( R Ro ) V Which is a straight line relation between cot(θ) and (R), have the slope = K / V and intersects the R-Axis at (Ro). 15 Method: 1. Connect the circuit as shown. 2. Adjust the galvanometer at the meridian position. Where the pointer is perpendicular to the coil. 3. Set the resistance to (R=10) from the resistance box. 4. Turn on the circuit. 5. record the deflections of the pointers θ1 and θ2 6. Reverse the current. 7. record the deflections θ3 and θ4 8. Calculate the average deflection θ = (θ1 + θ2 + θ3 + θ4)/4 and calculate Cot(θ) 9. Repeat the steps [5] to [8] with different values for (R). 10.Plot a relation between Cot(θ) and (R), Which is a straight line relation having the slope = K / V and intersects the R-Axis at (Ro). 11.From the intersection with R-Axis determine Ro From the Slope determine the radius of the coil (r). 12.To determine the unknown resistance (Rx), connect it instead of the resistance box and repeat the steps [5] to [8]. To obtain Cot(θ) for the unknown resistance and from the graph we determine (Rx) Results: Recorded Deflections R θ1 θ2 θ3 θ4 Average (θ) Cot(θ) = 1/Tan(θ) 16 Given Data V = 3 Volt Ho = 0.3 Orested N = 50 G= K = V · Slope = r= 17 Experiment No. (06) Comparison between the Magnetic Moments of Two Magnets using the Deflection Magnetometer General Case M1 d12 L12 M2 d 22 L22 2 2 d 2 tan 1 d1 tan 2 (1) Method 1. Put the magnetometer in Gauss first position, so that the two ends of the pointer are at the zero readings of the scale. 2. Put the first magnet (L1) on one arm at the magnetometers parallel to its scale at a distance (d1) between the middle of the magnet and the magnetometer center then read of the deflections (θ11 and θ12). 3. Put the same magnet on the same arm at the same distance (d 1) and chancing the poles of the magnet and read the deflections (θ13 and θ14). 4. Repeat the steps (2) and (3) for the same magnet at the same distance (d 1) on the second arm of the magnetometer and find the deflections (θ15 and θ16) and s (θ17 and θ18), then calculate the average deflection of the eight readings (θ1). 5. Repeat the steps (2-4) for the second magnet (M2) at different distance (d2) and find the average deflection of the eight readings (θ2) M1 M2 6. Calculate the ratio between the magnetic moments using Eq (1). 7. Repeat all the above steps for three different distances for each magnet and find the M1 M2 ratio in each case and then calculate the average value. 18 Results Table (1): For the first magnet Table (2): For the second magnet Table (3): Form Tables (1) and (2) we can write the final results as: 19