Chapter 17 Questions Flashcards
A 12V battery is connected across a device with variable resistance. As the resistance of the device increases, determine whether the following quantities increase, decrease, or remain unchanged: the current through the device
decreases
A 12V battery is connected across a device with variable resistance. As the resistance of the device increases, determine whether the following quantities increase, decrease, or remain unchanged: The voltage across the device
remains unchanged
A 12V battery is connected across a device with variable resistance. As the resistance of the device increases, determine whether the following quantities increase, decrease, or remain unchanged: the power consumed by the device
decreases - power is dissipated in the resistive device, but the electric current is not ‘used up’. the current entering the device equals the current leaving the device
remember power = V * I
To properly measure the current through a device, the ______ must be connected _______ with the device
ammeter, in series with
To properly measure the voltage across a device, the ______ must be connected ______ the device
voltimeter, in parallel with
In an analogy between traffic flow and electrical current, consider the following: What would correspond to charge Q?
the number of cars
In an analogy between traffic flow and electrical current, consider the following: what would correspond to current I?
the rate at which cars pass a given point
Two copper wires A and B have the same length and are conected across the same battery. If Rb = 6Ra, determine the following: the ratio of their cross sectional areas (Ab/Aa)
0.16667 -> higher cross sectional area = higher resistance
Two copper wires A and B have the same length and are conected across the same battery. If Rb = 6Ra, determine the following: the ratio of their resistivities
RESISTIVITY IS NOT RESISTANCE!!!
resistivity is a material property - both wires are copper, the ratio of the resistivity is 1
Two copper wires A and B have the same length and are conected across the same battery. If Rb = 6Ra, determine the following: The ratio of the currents in each wire (Ib/Ia)
0.16667 - know larger resistance = larger current also apparently
two lightbulbs are each connected to a voltage of 120V. One has a power of 25W, the other 100W. Which has the higher resistance? Which carries more current?
Resistance = 25W
Current = 100W
When is more power delivered to a lightbulb, immediately after it is turned on and the glow of the filament is increasing or after it has been on for a few seconds and the glow is steady?
when the glow of the filament is increasing
Consider positive and negative charges all moving horizontally with the same speed through the four regions in the figure below. Rank the magnitudes of the currents in these four regions from lowest to highest. For this question, know that BOTH negative and positive charges are counted and DO NOT CANCEL!!!
D, B, C, A
Suppose a current carrying wire has a cross sectional area that gradually becomes smaller along the wire, so that the wire has the shape of a very long, truncated cone. How does drift speed vary along the wire?
It speeds up as the cross section becomes smaller (electrons bounce off walls and eachother more often)
Suppose an electrical wire is replaced with one having every linear dimension doubled. How is the resistance of the wire affected?
The wire has less resistance than before - generally thinner, longer wires have greater resistance (R=pL/A)
