Physics 105 sample questions for Lab exam 1
Instructions: Your solution should show all relevant detail work and explanations.
1. A 36 cm diameter loop is rotated in a uniform electric field until the position of maximum
electric flux is found. The flux in that position is measured to be 5.0
electric field strength in this region. (Ans: 4.91x106 N/C)
105 N·m2/C. Calculate the
2. Two resistors, A and B, are connected in parallel across a 5.0 V battery. The current
through B is found to be 2.0 A. When the two resistors are connected in series to the 5.0
V battery, a voltmeter connected across resistor A measures a voltage of 3.0 V. Find the
resistances A and B. (Ans: A=3.75Ω and B=2.50Ω)
3. A charge particle remains stationary between the two charge plates with the top plate
negatively charge and the bottom plate positively charge. The plate separation is 2 cm
and m=4x10-13 kg and q=2.4x10-18 C for the particle. Find the potential difference
between the plates. (Ans: 32.7KV)
4. A 1.5V D cell, AC/DC Electronic Lab kit, a Multi-Meter, and resistors Ra=100 ohm, Rb=100 ohm
and Rc= 1000 ohm.
a. Design a DC circuit that has an equivalent resistance of 91.67 ohms using the three
resistors, draw a labeled circuit diagram and show the calculations for the equivalent
resistance. Assume that the positive terminal of the battery is connected on one end of
Ra and the negative terminal to the other end of Ra. (Ans: Req=91.67Ω)
b. Calculate (not measure) all the following currents and voltages across each resistor
(Show your detail calculations for example I500 = V/R = 2/500 = 0.004A,
V500=IR=0.004x500=2V etc).
I circuit Ans:0.016A
IRa (calculate) Ans:0.015A
IRb (calculated) Ans:0.0014A
IRc (calculated) Ans:0.0014A
VRa (calculated) = 1.5V
VRb (calculated) Ans:0.14V
VRc (calculated) Ans:1.4V
c. Build the circuit on the AC/DC Electronic Lab kit, and make a measurement on the
equivalent resistance of the circuit, using an ohmmeter. What is the measured value of
the equivalent resistance? And how does it compare with the given value.
Measured Requivalent = 90.23±9.17
d. Then measure (not calculate) the voltages across each resistor. Do not measure
currents. VRa Ans:1.5V
VRb Ans:0.135V
VRc Ans:1.34V
5. Use the equipotential and Field Mapper Kit, DC power source, an electrometer to answer the
following questions: The voltmeter is provided to check your circuit.
e. A schematic of the point source and a plate is provided on the separate sheet and on
the conductive paper. Setup the circuit and determine the configuration of the electric
field lines and the equipotential surfaces. Draw an accurate shape on the sketch
provided separately. Find the potential of one equipotential surface between the point
charge and the plate and near the +Q charge. Also find the potential of another
equipotential near the plate. Where will be the electric strongest and where will it be
nearly uniform.
+Q
-Q