Physics 2 Test 3
List two conditions for producing an electric current in a circuit.
(1) must supply a potential difference (2) must provide a continuous conducting path
Three identical resistors are connected in parallel to a battery. If the current of 12 A flows from the battery, how much current flows through any one of the resistors?
4 V
Three identical resistors are connected in series to a 12-V battery. What is the voltage across any one of the resistors?
4 V
When two or more resistors are connected in series to a battery
A) the total voltage across the combination is the algebraic sum of the voltages across the individual resistors. B) the same current flows through each resistor. C) the equivalent resistance of the combination is equal to the sum of the resistances of each resistor.
When two or more resistors are connected in parallel to a battery,
A) the voltage across each resistor is the same. B) the total current flowing from the battery equals the sum of the currents flowing through each resistor. C) the equivalent resistance of the combination is less than the resistance of any one of the resistors.
State Kirchhoff's junction rule.
At any junction point, the sum of all the currents entering the junction must equal the sum of all the currents leaving the junction.
A device that produces electricity by transforming chemical energy into electrical energy is called a
Battery
Consider two copper wires. One has twice the length and twice the cross-sectional area of the other. How do the resistances of these two wires compare?
Both wires have the same resistance.
As more resistors are added in series to a constant voltage source, the power supplied by the source
Decreases
The potential difference between the terminals of a battery, when no current flows to an external circuit, is referred to as the
Emf
A battery creates net electric charge.
False
A battery is responsible for supplying a constant current to a circuit.
False
A series circuit is a current divider and a parallel circuit is a voltage divider circuit.
False
An RC circuit is connected across a DC voltage source through an open circuit and a switch. As soon as the switch is closed, the charge on the capacitor increases but the voltage across it decreases as a function of time.
False
An RC circuit is connected across a DC voltage source through an open switch. As soon as the switch is closed, the capacitor charges linearly as a function of time.
False
Current in a metal wire is inversely proportional to the potential difference applied to its two ends.
False
If a fuse repeatedly blows, it should be replaced by a fuse of one step higher rating.
False
The fatter a given length of wire, the higher its resistance.
False
The resistance of most metals generally decreases with temperature.
False
The resistivity of the material of a wire is inversely proportional to the resistance of the wire.
False
Which of the following combinations would make a good analog ammeter?
Infinite
An RC circuit is connected across a DC voltage source through an open switch. The switch is closed at t = 0 s. Which of the following is a correct statement regarding the circuit?
Once the capacitor is fully charged, there is no current in the circuit
Outlets on a household circuit are arranged in
Parallel
The potential difference between the terminals of a battery, when current flows to an external circuit, is referred to as the
Terminal Voltage
You obtain a 100-W light bulb and a 50-W light bulb. Instead of connecting them in the normal way, you devise a circuit that places them in series across normal household voltage. Which statement is correct?
The 100-W bulb glows more brightly than the 50-W bulb.
The lamps in a string of Christmas tree lights are connected in parallel. What happens if one lamp burns out? (Assume negligible resistance in the wires leading to the lamps.)
The brightness of the lamps will not change appreciably
An RC circuit is connected across a DC voltage source through an open switch. The switch is closed at t = 0 s. Which of the following is a correct statement regarding this circuit?
The charge on the capacitor after four time constants is about 98% of the maximum value.
What happens to the resistivity of a typical semiconductor as its temperature increases?
The resistivity decreases.
Describe how a simple electric cell works.
The simplest cells contain two plates or rods made of dissimilar metals called electrodes. The electrodes are immersed in a solution, such as dilute acid, called the electrolyte. The part of each electrode outside of the solution is called the terminal, and connections to wires and circuits are made here. The acid tends to dissolve one of the electrodes, leaving it with a negative charge. As the electrolyte becomes positively charged, electrons are pulled off the other electrode by the electrolyte. Thus this electrode becomes positively charged. Because there is an opposite charge on the two electrodes, there is a potential difference between the two terminals.
State Kirchhoff's loop rule.
The sum of the changes in potential around any closed path of a circuit must be zero.
Consider two copper wires. One has twice the cross-sectional area of the other. How do the resistances of these two wires compare?
The thicker wire has half the resistance of the shorter wire.
Which one of the following is a correct statement for a number of resistors connected in series or parallel?
The total resistance in a parallel circuit decreases as more resistors are added.
Four unequal resistors are connected in a parallel circuit. Which one of the following statements is correct about this circuit?
The total resistance is less than the smallest resistor.
Four unequal resistors are connected in a series circuit. Which one of the following statements is correct about this circuit?
The total resistance is more than the largest resistor.
A 1200-W toaster draws more current than a 1000-W toaster.
True
A lightbulb cannot absorb charge.
True
As a dry cell ages, its internal resistance goes up.
True
Conventional current is the flow of positive charge from higher to lower potential
True
Four equal resistors connected across a DC voltage source in either series or parallel will have equal voltage drops across each resistor.
True
Four equal resistors connected in series have same current and same voltage across each resistor.
True
Four unequal resistors connected in series have same current but different voltages.
True
Kirchhoff's voltage rule is an example of conservation of energy.
True
The current in a circuit flows in the opposite direction to the direction in which the electrons move.
True
The electromotive force of a battery is the maximum potential difference between the terminals of the battery.
True
The longer a given diameter of wire, the higher its resistance.
True
A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. At the moment contact is made with the battery, the voltage across the capacitor is
Zero
A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. When this system reaches its steady-state, the voltage across the resistor is
Zero
If you connect two identical storage batteries together in series ("+" to "-" to "-" to "+"), and place them in a circuit, the combination will provide
Zero Volts
An ideal voltmeter is one that does not change the behavior of a circuit when it is properly used to measure potential difference. The internal resistance of such a meter is
a coil with a small resistance in series
Current flows through a resistor
from high potential to low potential.
The resistivity of most common metals
increases as the temperature increases.
An unknown resistor is wired in series with an ammeter, and a voltmeter is placed in parallel across both the resistor and the ammeter. This network is then placed across a battery. If one computes the value of the resistance by dividing the voltmeter reading by the ammeter reading, the value obtained
is greater than the true resistance.
An unknown resistor is wired in series with an ammeter, and a voltmeter is placed in parallel across the resistor only. This network is then connected to a battery. If one computes the value of the resistance by dividing the voltmeter reading by the ammeter reading, the value obtained
is less than the true resistance.
An advantage of a circuit breaker over a fuse is
it is easier to re-enable the circuit.
A galvanometer can be converted to an ammeter by the addition of a
small resistance in parallel
At very low temperatures the resistivity of some materials becomes zero as indicated by high precision measurements. This phenomenon is known as
superconductivity.
Materials in which the resistivity becomes essentially zero at very low temperatures are referred to as
superconductors.
Which of the following cylindrical wires has the largest resistance? All wires are made of the same material.
a wire of length L and diameter d/2
Decreasing the resistance of an ammeter's shunt resistance
allows it to measure a larger current at full scale deflection.
A current that is sinusoidal with respect to time is referred to as
an alternating current.
A wire of resistivity ρ must be replaced in a circuit by a wire four times as long. If, however, the total resistance is to remain as before, the diameter of the new wire must
be two times larger.
When resistors are connected in series
the current flowing in each is the same.
A current reading is obtained by properly placing an ammeter in a circuit consisting of one resistor and one battery. As a result,
the current flowing in the circuit decreases.
Kirchhoff's junction rule is a statement of
the law of conservation of charge.
Kirchhoff's loop rule is a statement of
the law of conservation of energy.
When resistors are connected in parallel, we can be certain that
the potential difference across each is the same.
If you connect two identical storage batteries together in parallel, and place them in a circuit, the combination will provide
the same voltage and twice the total charge that one battery would.
An ideal ammeter is one that does not change the behavior of a circuit when it is properly used to measure current. The internal resistance of such a meter is
0 Ω.
Three identical resistors are connected in series to a battery. If the current of 12 A flows from the battery, how much current flows through any one of the resistors?
12 A
Three identical resistors are connected in parallel to a 12-V battery. What is the voltage of any one of the resistors?
12 V
You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the largest possible resistance, you should attach the leads to the opposite faces that measure
3 cm × 5 cm.
As more resistors are added in parallel to a constant voltage source, the power supplied by the source
Increases
A voltage reading is obtained by placing a voltmeter across a resistor. What happens to the total current flowing in the circuit as a result of this action?
The current increases.
Consider two copper wires. One has twice the length of the other. How do the resistances of these two wires compare?
The longer wire has twice the resistance of the shorter wire.
A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. At the moment contact is made with the battery, the voltage across the resistor is
equal to the battery's terminal voltage.
If you connect two identical storage batteries together in series ("+" to "-" to "+" to "-"), and place them in a circuit, the combination will provide
twice the voltage, and the same current will flow through each
In order to construct a voltmeter from a galvanometer, one normally would
use a very large series resistor.
