Experimental Procedure 010 Things needed: 1. A cell or Battery (Energy Source) 2. A voltmeter to measure voltage across

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Experimental Procedure 010 Things Needed 1 A Cell Or Battery Energy Source 2 A Voltmeter To Measure Voltage Across 1 (83.52 KiB) Viewed 44 times

Experimental Procedure 010 Things needed: 1. A cell or Battery (Energy Source) 2. A voltmeter to measure voltage across the cell 3. A variable resistor or Load resistor 4. An ammeter to measure the current across the circuit 1 2 Circuit: • Connect all the above devices as per the circuit diagram Experiment / Measurements: Take readings of battery terminal voltage (V) for each step increment of current (1) with 0.6 (A). Adjust the resistance of your resistor box accordingly for current 0.6 (A) increment stepwise. (A) V.M Cell or Battery 0 6 0.6 5.76 & 1.2 5.52 13 5.28 2.4 5.04 Circuit Diagram Analysis MA gradient ar The terminal voltage is equal to IR so Eq.1 can be rearranged as: V=- Ir + E like y = mx + c When a graph plotted V against, I should give you straight line with gradient-r. I/A • The intercept on the y-axis is equal to the emf of the cell. • The gradient or slope of the plot is equal to -r and r is the internal resistance of cell emf is very important for electrical generators such as hydro dams, transformers used to boost the voltage. 1.)

EXPERIMENT E2 THE EMF AND INTERNAL RESISTANCE OF A SOURCE Aims The aims of the experiment are to determine: a) the emf, E, and internal resistance, r, of a cell; b) the condition for maximum power transfer. Method The small box provided contains a cell of emf & and internal resistance r. Using this cell, an ammeter (with negligible resistance), a variable (but known) resistance (R) and a plug key connect the circuit as shown below. Note the meter polarity ww Does it matter in what order the components are connected? Explain. In this experiment / is the dependent and R is the independent variable. Is this correct? Explain. Write down the equation for E in terms of the current, I, the external resistance, R. and the internal recictance of the cell E2.1 Show that equation (E2.1) can be rearranged into a form suitable for plotting a traight line oranh R+ IE E E2.2

E2,2 Explain what should be plotted against what in order to get a straight-line graph, and what you can determine from the slope and the intercepts on both axes. Is it necessary to show the origin on the graph if both intercepts are to be read off? Explain. Take current readings for values of R ranging from 2012 to 1002 in steps of 200, and then up to 400 12 in steps of 50 12. (Do not have R<2012, as this would draw too much current from the battery) Tabulate your readings and the quantities that you calculate from them in the table below. You should convert the milliammeter readings to amperes. Included also is a column for the power dissipated in the external resistance P=°R. R (92) I (mA) P=1 R(W) 20 75.3 40 66.0 60 60.3 80 53.4 100 48.8 150 41.5 200 35.2 250 28.2 300 20.0 350 13.1 400 0.0

Analysis (a) Plot the straight-line graph suggested by equation (E2.2). N.B. Make sure that you can read a sufficiently large negative intercept on the R axis. From the graph, showing your calculations, determine & and the latter in two ways). (b) Plot P against R. Determine the value of R for which P is a maximum. Compare this value with that of r. What do you conclude from this comparison? Explain whether or not this graph should go through the origin,