MCD 1200 Lab 3 More Circuits Record Data-2 PDF

Preview

Summary

Download MCD 1200 Lab 3 More Circuits Record Data-2 PDF

Description

Lab Work MCD 1200 LAB 3: More Circuits Student Name: Student ID: Tutor’s Name: Tutor’s Sign Marks

/15

1/9

Part A: Resistance and Capacitance in Series When a voltage is applied to a circuit containing a capacitance, C, and resistance, R, it takes a finite time for the charge to build up on the capacitor plates. The time required for the capacitor to become fully charged is approximately 5 RC (in second), i.e. 5 times the TIME CONSTANT RC. Charge moving in the circuit constitutes a current, so when the voltage is first applied a large current flows but then it gradually drops towards zero as the capacitor becomes charged. Again, it takes about 5 RC for the current to return to zero. Charging

Discharging

V =V 0 e−t / RC 1RC =

1RC = 5RC =100% = Full Charge

5RC =100% = Fully discharge

12 V

Figure 1

PART I (with C=100µF) 1. Charging : Step 1: Switch off the circuit Step 2: Connect the circuit as per Figure 1.

2/9

Step 3: What is the expected value of the time constant in this circuit? (You can neglect the resistance of the ammeter and power supply). Your Prediction = RC Step 4: Set the power supply to give 12 V – the output is between the upper red (+) and lowest (-) terminals. Step 5: Watch the current reading on the multimeter as you turn on the power supply; Until multimeter reading returned to zero. Take a video on your phone (as it changes very quick).

Step 6: Complete Table (refer to your video to get the readings)

Step 7: Roughly sketch the current as a function of time for this part of the experim ent.

Step 8: Plot it using spreadsheet (Excel) and write the equation of charging from Excel Equation:

Time (Sec)

2. Step out not

Current (mA)

1 2 3 4 5 6 7 8 9 10

Discharging: 1: (Do NOT switch power supply off before pulling leads). Remove the leads from the power supply and do touch the leads yet

Step 2: Now touch leads together, watching the current on the multimeter. Record the reading on multimeter until the reading becomes zero. Take a video on your phone (as it changes very quick). Step 3: Complete Table (refer to your video to get the readings)

Step 4: Roughly sketch the current as a function of time for this part of the experim ent.

Step 5: Plot it using spreadsheet (Excel) and write the equation of discharging from Excel Equation:

Time (Sec)

Current (mA)

1 2 3

3/9

4 5 6 7 8 9 10

3. Switch power supply off; connect the leads back into the supply terminals. Then charge and discharge the capacitor as in the previous section, but this time use the timer to measure how long before the current becomes steady (or zero) for both the charging and discharging situation. This time is approximately 5RC. Are the values for charging and discharging approximately the same? Compare the measured value with the value of the time constant RC expected from theory. Comment on your readings. Results Charging Dischargin g

Theory

Experimental

Compare and Comment

4/9

PART II (with C=1100µF)

12 V

Figure 2 Step 1: Switch the power supply off. Step 2: Connect the leads back into the supply terminals as before. Now connect the 1000 μF capacitor in parallel with the 100 μF capacitor already in the circuit. (Note, connect the end marked + to the more positive part of the circuit, i.e. to the ammeter. This is required to maintain the non-conducting film between the plates inside the capacitor.) Step 3: Measure the time for charging to take place using the technique of section 2 and estimate the expected time constant of the circuit using two capacitors? Your Prediction =

RC

Step 4: Explain your result in (A4) above. It may help to consider the effective capacitance when two capacitors are connected in parallel, as if they were one larger capacitor. Charging Time (Sec)

Current (mA)

1 2 3 4 5 6 7 8 9 10

5/9

Discharging Time (Sec)

Current (mA)

1 2 3 4 5 6 7 8 9 10

Step 5: With the power supply left turned on, the current fall to zero. Disconnect the leads from the power supply and let them sit on the bench, without touching anything, for about 90 seconds. Then touch those two leads together and observe the multimeter.

Step 6: Describe and explain what happens (remember that you waited some time before connecting the leads together).

Results Charging Dischargin g

Theory

Experimental

Compare and Comment

6/9

Look at the unit Equation 1

q=CV q Columbs C= = =Farad (F) V voltage V =IR V Voltage =Ohms (Ω) = R= Ampere I Q Columbs I= = = Ampere( A) t sec

Unit of RC =

Voltage x Ampere ¿

Equation 2

Equation 3

Columbs voltage

Columbs Ampere

= Columbs x

sec Columbs

¿ sec

R = 10 kΩ C= 100 µF

R = 10 kΩ C= 1100 µF

Calculation: 5 RC

(Do the Calculations, and show here) 5RC

= 5 ( 10 kΩ) (100 µF ) = 5 (10 x 103) (100x10-6) = 5 sec

7/9

Part B – Magnetic Induction

Figure 3 The oscilloscope is a very important measuring instrument. The vertical deflection of the trace is proportional to the input potential difference (PD or voltage) and the trace moves horizontally at a constant rate (which can be set) to display a graph of emf induced in the coil versus time. 1. Connect the terminals of the coil to the input of the oscilloscope. Place the rod through the coil so that the magnet is out and clear of the far end of the coil. Turn the rod so the magnet sits on top of it. Observe the oscilloscope trace when the rod is rather quickly drawn into the coil, and again when it is drawn completely out (of the right hand side for the above diagram). Once you can move the magnet fairly smoothly and readily see the trace deflections, proceed to the detailed observations below. (L = ‘left’ and R = ‘right’ in the instructions below). 2. For the following, observe and sketch the relative size and direction of the trace deflections. Explain the behaviour of the induced emf in the coil using Faraday’s and Lenz’s Laws. You will not be able to predict the sign of the emf in an absolute sense as you do not know the direction the coils are wound, but you can do the comparisons required in (a) and (b) below.

8/9

Try following activities

A. Moving the magnet rather slowly into the coil compared to movement in the same direction done quickly; B. Move magnet into the coil (L to R) compared to moving the magnet out of the coil (R to L) at about the same speed; C. Move the magnet back and forth about 2 cm around the middle of

the coil fairly quickly. The magnet should not get to close to either end.

9/9

-----------------------------------------END OF THE LAB------------------------------------------

10/9...