Practical Physics Laboratory Lectures, Part 2 - Al-Mustafa University College, 2023-2024 PDF

Ministry of Higher Education and Scientific Research Al-Mustafa University College Practical physics laboratory lectures Part (2) BY Dr. Nisreen Khalid Fahad 2023-2024...

Ministry of Higher Education and Scientific Research Al-Mustafa University College Practical physics laboratory lectures Part (2) BY Dr. Nisreen Khalid Fahad 2023-2024 1 Object Verify Boyle's Law by measuring the pressure of the atmosphere. Apparatus: Glass tube containing mercury as shown in figure (1). Theory: The equation used to find the atmosphere pressure is 𝑪 𝟏 H= × − 𝑩 ------------ (1) 𝑲 𝑳 Where: C& K: Constant. H & L: the length as shown in figure (1). B: Atmosphere Pressure. 2 Procedure: 1) Keep the mercury levels X and Y in the same position, Record the scale reading of these levels and also the scale reading of (A), the inside of the closed end of the tube (AB). This is the balance point (i.e. X = Y). 2) Rising the tube CD (above the balance point), and record the scale reading of X and Y levels. 3) Take about four sets of reading over the balance point 4) Now, lower the tube CD below the balance point, and record the scale reading of X and Y levels 5) Take about four sets of reading below the balance point Readings and calculations: 1) Arrange the result in the table. 2) Plot a graph for the values of h (cm) as ordinates against the corresponding values of 1/L (cm-1) as abscises. 3) If the plot of h against 1/L yields a straight line, Boyle's law is verified and the negative intercept on the h-axis is numerically equal to B (atmospheric pressure Barometric height = 76 cm). 4) from the graph; if h = 0, find the value of 1/L =? B = 76 cm. Find the value of C/K from equation (1). 3 Object To determine Joule's constant (J) or the mechanical equivalent of heat by electrical method. Apparatus: An electric calorimeter, a DC power supply (high power), an ammeter, a timer, a glass beaker, an equal arm balance with weights Theory: In this experiment, heat is produced by passing a current through a resistor which is immersed in a container of water. The purpose of this experiment is to compare the energy dissipated by the resistor to that absorbed by the water, thereby testing the principle of conservation of energy. When an object is heated, the transfer of energy Q to the object increases the object’s temperature, ΔT, according to the relationship Q = mcΔT …… (1) where m and C are the mass and specific heat of the object When a potential difference is applied across a resistor, a current pass through the resistor resulting in the generation of heat (Joule heating). The rate at which the resistor dissipates the energy (the heat) P is P = V I ……….. (2) where V is the potential difference across the resistor, and I is the current passing through the resistor, after an amount of time t has elapsed, the energy E dissipated in the resistor is E = P t = V I t………….. (3) 4 If I in ampere and R is in ohm, then P is in watts. In a time, interval Δt (in seconds) an amount of energy ΔE=P · Δt (in joules) will be released, in the form of Joule Heat. The released heat is absorbed by the core of the calorimeter OR The amount of absorbed heat ΔQ (within a time Δt) is given by relation (4) where: ΔQ = (MW·CW+MCal·Ccal) ·ΔT………. ….. (4) Mw = mass of the water = 178.84g Cw = specific heat of water = 1 cal/g.c Mcal= mass of the inner cup and stirrer of the calorimeter Ccal = specific heat of the inner cup and stirrer = 0.385 cal/g.c ΔT = change in temperature during the time interval Δt This applies if MW and Mcal are in grams, ΔT is in degrees Celsius (OC), and CW and Ccal are in cal/gm. C. Procedure 1) Determine the mass Mc of the calorimeter cup and record it in the Data 2) Place enough water (about 150-200 mL) in the calorimeter cup to immerse the resistor coil completely. The water temperature should be a few degrees below room temperature. Be sure that the coil is completely covered by the 15 water, but do not use any more water than is necessary. Determine the mass of the water plus the calorimeter cup and record it in the Data 3) Determine the mass of the water by subtraction and record it as Mw 4) Connect the circuit as shown in below figure 5 5) Adjust the power supply to a current of 15V. Record the voltmeter and ammeter readings. 6) Record the initial temperature Ti and at the same time turn on the stopwatch. 7) Estimate the thermometer readings at (40, 80, 120, …600) s for all temperature measurements. 8) Stir continuously and let the temperature rise about above the initial value. Record the elapsed time, t, and the final temperature Tf Calculations: 1) Calculate the quantity mc, where MC = MwCw + McCc 2) Calculate the temperature rise of ΔT above the initial temperature Ti from ΔT = Tf– Ti for each of the measured values of T and record the results in the Calculations Table 3) Plot a graph of ΔT (Y-axis) against t (X-axis). 4) Calculate the specific heat of water using equation (5) 5) Calculate the error percentage between your result and the known value of 4.186 J / cal. 6 Object: To measure the speed of sound using the concept of resonance; to determine what, if any, effect varying the frequency of a sound wave has on the speed of that sound wave. Apparatus: Set of tuning forks in the frequency range 256 Hz to 512 Hz, water, 1000 ml graduated cylinder, thermometer, ruler Theory The basic idea behind this experiment is to generate sound waves of known frequency inside Kundt’s tube apparatus and find the locations of nodes. Distance between two consecutive nodes being λ/2 we can obtain wavelength this way and hence the velocity of sound. We can find the locations of nodes as we scan the length of the vibrating air column using a microphone. For a sinusoidal wave with constant frequency f and wavelength λ, propagating in a medium, the speed of sound in said medium is given by: ʋ = λf ………. (1) This means that if we can determine both the frequency and wavelength of the wave, we can measure the speed of sound in the medium. For this experiment, the medium in question is air at room temperature and atmospheric pressure. Sound is a longitudinal wave. A wave consists of an oscillation in some medium. Ocean waves are transverse waves in water. (The water molecules oscillate perpendicular to the direction of propagation of the wave.) Sound waves are longitudinal waves in air. (The air molecules oscillate in the direction of propagation of the wave). 7 Procedure 1) Fill the tube and the water supply container with water from the water can until the water level in the tube is within 10 cm of the top of the tube. Be sure that the container is not full, because the container will be lowered, and water will flow into the container. 2) Hold the thermometer in the tube and measure the temperature, T, of the air 3) Hold several tuning fork with different frequencies (256, 288, 341, 426, 512) Hz at its yoke and either strike the tines with the rubber mallet or strike the tuning fork on something soft. Hold the tuning fork over the open end of the tube and slowly 4) lower the water level in the tube by lowering the water supply container until resonance is achieved, the water level in the tube now represents the position of a node. Record the water level position, 5) Arrange you results as shown in table below: 6) Plot a graph of (L) on (y-axis) as a function of (1/F) on (x-axis). Then find the slope that represents (F×L) 7) Determine the speed of sound by the following relation: C = 4×slope…………. (2) 8 Object To study the diffraction of the laser by a single narrow slit. Apparatus: Laser source (diode laser) of wavelength λ =(630nm), Screen, Single slit, Ruler. Theory: Laser is an electromagnetic radiation produced by light amplification of stimulated emission of radiation. It has all the characteristics of light and the law, of reflection and refraction. Laser has the following characteristics: 1) It is coherent light i.e. the photons of a laser beam have the same frequency, direction, and phase. 2) It has very high intensity. 3) It has very low diffraction. 4) It can be used as a continuous or pulse wave depending on the kind of source and the required application for example pulse waves are normally used in medical applications. 5) It can deliver large energy in a very short time. 6) It can be transmitted through optical fibers to minimize the diffraction of laser i.e. to minimize the waste of laser energy and also it can be transmitted through flexible fibers to different parts of the body from different openings like mouth, nose.... etc. 9 Procedure: 1) Switch on the laser apparatus and notice the red beam of the laser. 2) Arrange the slit so that the laser will be transmitted through the slit and incident on the screen. 3) Move the screen forward and backward until you get the clearest fringes on the screen. 4) Measure the distance between the center of the central fringe and each of the bright fringes. 1st fringe(X1), 2nd fringe (X2)............... as follows: 5) Apply Snell law: n λ = d sinθ but θ is very small therefore sinθ ≈ θ 𝑿 𝒏 𝒅 nλ=d → 𝛌= 𝑫 𝑿 𝑫 𝒏 Slope = 𝑿 d = width single slit. D = distance between the slit and screen. D = 104 cm 10 Object To find, the focal length of a convex lens Apparatus: Convex lens, optical bench, light source, target image slide, Screen. Theory: A lens is a transparent medium bounded by two refracting surfaces. Lenses are used in optical instruments such as cameras, telescopes, and microscopes. When parallel light rays pass through a thin lens, they emerge either converging or diverging. The point where the converging rays (or their extensions) cross is the focal point of the lens. The focal length of the lens is the distance from the center of the lens to the focal point. If both sides of the lens curve outward, it is called a converging lens, and it will bend light from distant objects inwards. Toward a single point, called the focal point If both sides of the lens curve inward, it is called a diverging lens, and light from distant objects will bend outwards. 11 In actuality, there are two focal points for every lens, the same distance from the lens, on opposite sides. For converging lenses, the focal length is always positive, while diverging lenses always have negative focal lengths. The lenses are used in many things, they are used in the medical eyeglasses either for reading or walking and the lenses are used in Microscopes which are used for formation magnified images of the tiny bodies that cannot be seen with the naked eye and they are used in making of medical glasses to treat the vision defects. An image formed by a convex lens is described by the lens equation: Where u is the distance of the object from the lens; v is the distance of the image from the lens and f is the focal length, i.e., the distance of the focus from the lens. 12 Procedure: 1) To find the focal length (f) for the convex lens align all components in same height as shown in below Fig. 2) Move lens (L) back and forth till a clear image of the object on (P) is observed on the screen. 3) Measure the distance between the object (P) and leans(L) and also the distance between the lens and screen (u and v respectively) starting with (u=10 cm). 4) Move the lens by increasing the distance (15, 20, ….35) cm to obtain another clear image and record the results. 5) Arrange your results as shown in the table below: 6) Plot a graph of (uv) on (y-axis) as a function of (u+v) on (x-axis). then find the slope that represent focal length (f) Slope =f= uv/u+v Discussion: 1) What are the most likely sources of error in this experiment? 2) List some everyday things that use lenses. 3) Which convex lens has more focal length, thick or thin 13