Current & Resistance, Power & Brightness
What is the equivalent resistance for these resistors between points a and b?
(Diagram on Slides)
13.7 ohms
W23 Phys 2B Final Exam, Q5
For the following circuit diagram, what is the power dissipated by the 6Ω resistor?
(Diagram on Slides)
3.17W
Prelecture 25C, slide 15-19
A student is conducting experiments in lab with a simple RC circuit. The capacitor and resistor values are unknown. She charges up the capacitor with a voltage source, Vo, until it is fully charged and then disconnects the voltage source from the circuit. A switch is then closed and she measures the voltage across the capacitor as it discharges through the resistor. The measurements are made every half a second, as shown in the graph below.(Diagram in slides)
Use voltage formula for discharging capacitor in an RC circuit.
Find initial voltage (36V) and voltage at a certain point (ex: 4V at 5.5s)
RC = 2.5s
Sample Exam #2, Q5
A circular coil of wire is positioned perpendicular to an external magnetic field that is directed into the page. The external magnetic field is then suddenly increased. What direction in the wire will the resulting induced current be?
(Diagram on Slides)
CCW
W23 Phys2B Final, Q3
Two light bulbs, one 30 Ω and the other 60 Ω, are connected in parallel to a 120 Volt battery (all three circuit elements are in parallel). In this situation:
(Diagram and options on slides)
Option A
W23 Phys2B Final Exam, Q9
What is the voltage drop across the 4.0 ohm resistor (in Volts)?
What is the power dissipated by the 12 ohm resistor (in Watts)?
(Diagram on Slides)
1) 4V drop
2) 3W dissipated
W23 Phys2B Final Exam, Q14-15
Consider an electron 10.0 μm away from a wire with a current of 200 A directed downwards. The electron moves to the left at a velocity of 50,000 m/s.
What is the magnitude and direction of the magnetic force on this electron (in N) due to this wire?
(Diagram on Slides)
Calculate magnetic field: 4.01T
Use mag field to get mag force: 3.2*10^(-14) N
Direction of force: Up
W23 Phys2B Final Exam, Q10-11
You are analyzing an inductor (part of a bigger circuit). You note that the voltage at point a is 25 Volts and the voltage at point b is 50 Volts (as shown in the figure below) at a particular point in time. What direction is the current flowing in, and is it increasing or decreasing or staying the same?
(Diagram on Slides)
Current flowing from point a to b, decreasing
Sample Exam #2, Q7