Download Electricity Review questions and Study guide Types of problems for

Electricity Review questions and Study guide
Types of problems for Electricity Unit:
Determine electrical forces using Coulombs law. Vector problem TH
Determine electric field due to charges. Vector problem. TH
Sketch Field diagram showing field lines and equipotential lines.
Determine current in a wire due to moving charges. Definition of current = charge/time. I=nqAv
Resistance in wires. R = L/A
Ohms Law
Simple Series and Parallel circuits to solve. TH
Combined Circuit TH
Circuits with real batteries TH
Kirchoff Laws circuit TH
Determine electric potential due to charges. Scalar problem.
Relate potential to work.
Relate potential to electric field. Especially between parallel plates.
Too many time consuming problem solving type questions to assess within a 90 min class period. Therefore the
Electricity test will be two part. 1/2 in-class for Feb 28, and 1/2 take-home due beginning of class Mar 2.
Topics for the Take Home portion are the more time consuming problems indicated with TH above. All other
types of problems will be included in the classroom assessment.
Expectations for take home exam: Honor code that work submitted is your own work representing your own
understanding of the problems presented. You may use any online resources, textbook or notes to help you, but
you may not discuss your solutions with other people or work together on your solutions. You should not share
the answers you obtain in any way. If you find a particular resource helpful, you may share that information.
Sample problems:
1. Four charges are arranged in a square with sides of length 3.50 cm. The charges in the top right corner is
+2.0 μC and bottom left corner is +4.0 μC. The charges in the other two corners are both –3.0 μC. What
is the net force exerted on the charge in the top right corner by the other three charges?
2. For the charge distribution described in #1, what is the electric field at the center of the square?
(magnitude and direction)
3. A +2 μC charge is located 5.0 cm away from a –2 μC charge. Sketch the electric field lines and the
equipotential lines around these two charges.
4. During a 4.00 min interval, a 1.35 A current is set up in a wire. How many a) coulombs and b) electrons
pass through any given cross section across the wire’s width?
5. A small but measurable current of 1.23 x 10-10 A exists in a copper wire whose diameter is 2.50 mm.
The number of charge carriers per unit volume is 8.49 x 1028 m-3. Assuming the current is uniform,
calculate the electron drift speed.
6. Section 1 of a wire has a diameter D1 = 4.00R. Section 2 of the wire has a diameter of 2.00R. The two
sections are connected by a tapered region. The wire is copper and carries a current. Assume that the
current is uniformly distributed across any cross-sectional area through the wire’s width. The electric
potential change V along the length L = 2.00 m for section 2 is 10.0 mV. The number of charge carriers
per nuit volume is 8.49 x 1028 m-3. What is the drift speed of the conduction electrons in section 1?
7. A copper wire of cross sectional area 2.00 x 10-6 m2 and a length of 4.00 m has a current of 2.00 A. The
resistivity of copper is 1.70 × 10-8  m. a) What is the resistance of the wire? b) What is the magnitude
of the electric field along the wire? c) What is the power dissipated by this wire? d) How much
electrical energy is transferred to thermal energy is 30 min?
8. Three resistors are connected in series to a 15 V battery. If R1 = 25 , R2 = 16 , and R3 = 40 ,
determine the current and potential for each battery and the current ant total resistance for the battery.
Repeat if the resistors are connected in parallel.
9. Solve the following circuit completely.
10. Determine the current present in each battery and resistor. Indicate the direction of each current on the
diagram.
11. A charge of –1.50 μC is located on the positive y-axis of a coordinate plane 20.0 cm from the origin
while a second charge of +2.50 μC is located on the positive x-axis 10.0 cm from the origin. Determine
the value of the following quantities at the origin.
a. the magnitude of the electric field,
b. the direction of the electric field,
c. the electric potential (assuming the potential is zero at infinite distance), and
d. the energy needed to bring a +1.0 μC charge to the origin from infinitely far away.
12. Two large, parallel, conducting plates are 12 cm apart and have charges of equal magnitude and opposite
sign on their facing surfaces. An electrostatic force of 3.9 x 10-15 N acts on an electron placed anywhere
between the two plates. a) Find the electric field between the plates. b) What is the potential difference
between the plates? c) If the electron approaches the positive plate perpendicular to the plane of the plate
at 3.5 x 105 m/s, determine the speed and direction of the electron when it reaches the midpoint between
the plates. d) What is the speed of this electron when it reaches the negative plate? e) If the electron
approaches perpendicular to the negative plate at 3.5 x 105 m/s, what is it’s speed when it reaches a point
half way through? f) What is the speed of this electron when it reaches the positive plate?