Hooke's Law, Osmosis in Potato Slices PDF

Hooke's law Purpose : To investigate experimentally the extensionof a spring and how it is related to the applied force, and recall that the extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. The main variables in...

Hooke's law Purpose : To investigate experimentally the extensionof a spring and how it is related to the applied force, and recall that the extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. The main variables in a science experiment are the independent variable,the dependent variable and the control variables.  Independent Variable is the stretching force F. This is the weight attachedto the spring and is calculated using W = mg.  Dependent Variable is the extension of the spring e.  Control Variables are the material of the spring, and the cross section are of the spring. These are kept the same by not changing the spring during the experiment. Remember - these variables are controlled (or kept the same) because to make it a fair test, only 1 variable can be changed, whichin this case is the stretching force (i.e. the weight attached to the spring). Hooke's law: The extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. The equation for Hooke’s Law is: F =- k ΔL, ΔL=L-L˳  F is the force in newtons (N)  k is the 'spring constant' in newtons per metre (N/m)  ΔL is the extension in metres (m)  L is the extention of the spring  L˳is the length of the spring in relexed state(without any force applied) Apparatus A steel spring, masses, 20,30,40…gm, Weights holder , a metre rule,. Method: 1. Set up apparatus as shown in the diagram. 2. Attach the mass hanger s -hook and pointer to the lower end of thespring. The pointer should just touch the metre rule. 3. Read the pointer value from the metre rule. Record this length in a suitable table. This is the initial length of the spring for zero mass. Wecan neglect the mass of the hanger. 4. Add a 20 g slotted mass to the hanger. Record the mass in kg in thetable. 5. Read the new position of the pointer on metre rule. This is the stretchedlength of the spring. Record this length in the table. 6. Calculate the stretching force = weight of masses: W = mg. 7. Calculate: extension = stretched length – original length. 8. Repeat the procedure by adding 20g masses Record the new stretchedlength by reading the position of the pointer on the metre rule. Subtract the original length from the new stretched length to calculate each extension. Trial masses (gm) F=mass(kg)*g ΔL=L-L˳ 1 2 3 4 5  Osmosis in Potato Slices Osmosis is a special case of diffusion, and refers specifically to the diffusion of water. Water molecules can move in and out of cells in vegetables, flowers, and animals) including people). The cell wall is like the balloon membrane. water can move INTO and OUT OF a potato slice cause it contain water and minerals. One of the minerals in a potato is SALT. Distribute two slices potato to each group Apparatus 1 Potato Activity Sheet, one 100 mL beaker of distilled water, 1 container of salt, 1 spoon, 1 petri dish and lid labeled #1- water, 1 petri dish and lid labeled #2- salt, 2 rectangles of potato.  Method Preparation: 1.Place the 2 petri dishes on the appropriate sections of the Potato Activity Sheet. 2.Pour distilled water into the two small cups, to the 30 mL mark. 3.Place the 2 petri dishes on the appropriate sections of the Potato Activity Sheet. 4.Very carefully feel how rigid or floppy the potatoes are. (NOT break them.) Precedure: 1. Trace one of the pieces of potato on the first section of the Potato Activity Sheet and place it in the bottom of the petri dish that is next to its tracing. 2. Pour distilled water from one of the cups into this petri dish #1, so that the potato slice is completely covered and place the lid over the petri dish. 3. Make the salty water by putting 1 tsp of salt into the other 3.5 ml cup and stirring until it is dissolved (it will not matter if there is some solid remaining). 4. Trace the other piece of potato on the second section of the Potato Activity Sheet. 5. Place it in the bottom of the petri dish #2, which is next to its tracing. 6. Pour the salt solution into this petri dish #2, so that potato slice is submerged and place the lids over the petri dish. 7. Record the Start Time at the top of the page. After 25 minutes, do the following:  Remove the first potato slice from the water and very gently blot it on a paper towel.  Fit the potato to one short end of the original trace (rather than a long end) and note changes in the length.  Repeat with the other potato slice. Results The potato slice in the water is larger, indicating that more water molecules went into the potato than came out, because there was a higher concentration of water outside of the potato. The potato slice in the distilled water is longer (and wider), indicating that more water molecules went into the potato than came out. The potato is also stiffer. The potato slice in the salt solution is shorter (and thinner), indicating that more water molecules came out of the potato than went in. This potato is very limp.  Demonstrate Diffusion with Hot and Cold Water Diffusion is a movement of particles from the area of high concentration to an area of low concentration. It usually occurs in liquids and gases. Diffusion is a type of passive transport. That means it doesn’t require energy to start. It happens naturally, without any shaking or stirring. Theory: All fluids are bound to the same physical laws – studied by Fluid mechanics, part of the physics. usually think of fluids as liquids, but in fact, air and other types of gas are also fluids! By definition, fluid is a substance that has no fixed shape and yields easily to external pressure. Apparatus: 2 transparent glasses – Common clear glasses will do the trick. You probably have more than needed around the house. We need one for warm water and one for cold water so we can observe the difference in diffusion. Hot and cold water – The bigger the difference in temperature in two glasses, the bigger difference in diffusion will be observed. You can heat the water to near boiling or boiling state and use it as hot water. Use regular water from the pipe as “cold water”. That is enough difference to observe the effects of temperature on diffusion. Food coloring – Regular food coloring or some other colors like tempera (poster paint) will do the trick. Color is required to observe the diffusion in our solvent (water). To make it more fun, you can use 2 different colors. Like red for hot and blue for cold. Methods: 1. Take 2 transparent glasses and fill them with the water. In one glass, pour the cold water and in the other hot water. near-boiling water for hot and regular temperature water from the pipe will be good to demonstrate the diffusion. 2. Drop a few drops of food coloring in each cup. 3-4 drops are enough and you should not put too much food color. If you put too much, the concentration of food color will be too large and it will defuse too fast in both glasses. 3. Watch closely how the color spreads. You will notice how color diffuses faster in hot water. It will take longer to diffuse if there is more water, less food color and if the water is cooler. Results: color diffuses faster in hot water than cold water.  Wheatstone bridge Objective : The aim is the determination of unknown resistance by using the Meter Bridge. It could be also used in determination of resistivity of a metallic wire Theory:  ρ = R1wire A/L Where  A =πr2area of the wire,  r is the radius and  L is its length For meter bridge:  R1 is the unknown resistance  R2 is the known resistance  ℓ1 distance between the slider and A  ℓ2 distance between the slider and C methods :  Connect the circuit as shown in Figure  Get the balance condition by moving the slider on the meter wire until the reading in the digital multi meter is zero.  measure the lengths l and l ’ (l ’=100)  Calculate the unknown resistance R’wire  find the resistivity from ρ = R’wire A/L Apparatus: Unknown resistance, Power supply, Known resistance, Meter Bridge set of 1 meter long  Archimedes principles Objective:  To verify Archimedes principles  To measure any liquid density Theory: If we have a body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward force , or buoyant force. the magnitude of which is equal to the weight of the fluid displaced by the body. Method : 1. Attach a metallic weight to the spring and record the spring length in the air 2. Put a glass beaker containing a sociable amount of water and decade the spring gradually until the hanged weight is completely submerged in water such that the solid body doesn’t touch the wall or the bottom of the backer and record the spring length. 3. Record the volume of the immersed weight which equals the weight displaced water V=πr2 4. Calculate the buoyant force from the relation Fb=k∆L 5. Repeat previous steps but every time increases the number of attached to the spring 6. Tabulate the values of v and ∆L and plot the graph between them straight line 7. Calculate the slope of the straight line which will be Slope =∆L/V From the buoyant force equation : fb =ρ v g 8. Calculate the density : ρ= ∆ / / which equal 1 gm/cm^3  Ohm law Objective :  Verification of ohm s law. Theory: The current (I) passed through a conductor is directly proportional to voltage (V) across that conductor at constant temperature V&I V= IR Potential Work done to Volt Voltmeter move difference the coulomb from one point to another Amount of Ambere Electric current Ammeter charge c/s passing through certain section of conductor per second Degree of Ohm Ohmmeter Resistance opposition that a Ω material body oppose passage of electric current Procedure  Connect the circuit  Vary the electric current and record the  voltage across the conductor  Repeat step 2 about 5 times  Tabulate the result  Draw graph between v & I  The relation between a v& I  Magnetometer Purpose: To set magnetic moment Materials:  Magnetometer (Ruler /Compass(  Magnet Procedure: 1. Make sure the Magnetometer reached its stable state. 2. Bring the magnet close to the compass to move thecompass needle. 3. Take the angles of the compass as Ɵ1&Ɵ2. 4. Calculate the angles average. 5. Calculate thecot. 2 6. use 3 = Note is the magnetic moment  7. Calculate the slope Results 3 Ɵ1 Ɵ2 AverageƟ cot  Measurement of Viscosity by Stokes’s Law Theory η is the liquid viscosity…………….……. (gm cm-1 sec-1) or (Kg m-1 sec-1) r is the radius of ball ……….…….……….(cm) ᴠ is the terminal velocity ………………. (Cm/sec) is the density of the ball ……………. (g/m3) is the density of the liquid ………….. (g/m3) g is the acceleration due to gravity …..(cm/sec2) the force acting on the ball is: = m g = V g= The up thrust FU due to the displaced fluid FU = m g = V g= The viscous drag force FS which is given by stokes’s law Apparatus A glass cylinder metallic spherical ball Digital stopwatch Method Fall the metallic ball in the liquid. The time taken for the ball to fall from mark ( A )to mark (B) is determined by the stopwatch. Letting A is sufficiently far below the surface so the ball will reach its terminal velocity before reaching( A). From the above time calculate ᴠ by using the equation ᴠ = d/t. Using the constants , , r and g to calculate η for the fluid.