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Physics midterm 2

Terms in this set (32)

What is the direction of the conventional electric current in a circuit?
-From high potential to low potential
-From positive to negative
-Opposite the direction that electrons move through the circuit
Which of the following is the best statement of Ohm's law?
The current in a metal wire is proportional to the potential difference applied to its two ends
What is the advantage of using the rms values of current and voltage?
-For circuits containing only resistive elements, using the rms values allows us to use the same equations for AC circuits as for DC circuits
-The rms values are not zero while the average (mean) values are zero
The resistance of a wire depends on which of the following? Assume the wire is ohmic.
-The length of the wire
-The thickness of the wire
-The material from which the wire is made
-The temperature of the wire
Below the critical temperature the resistivity of a superconductor..
Is exactly zero
What is the main reason that the terminal voltage of a battery is not independent of the current in the circuit?
A real battery has internal resistance
When is the potential difference of a real battery equal to its emf?
When there is no current through the battery
A real battery has an emf of 6 V and an internal resistance of 1 ohm. What is the terminal voltage of the battery when it has its maximum possible current through it?
Zero
Which of the following are necessarily true about resistors in series?
-The current is the same through each resistor
-All the resistors are in the same branch of the circuit
-The total voltage equals the sum of the voltages across each resistor
Which of the following are necessarily true about resistors in parallel?
-The potential difference (voltage) is the same across each resistor
-Each resistor is in a different branch of the circuit
-The total current equals the sum of the currents through each resistor
A fully charged capacitor is connected to a resistor and a switch which is initially open. When the switch is closed..
The current decreases exponentially
Which of the following statements is true for capacitors in parallel?
The potential difference must be the same across each capacitor
Which of the following statements is true for capacitors in series?
The charge must be the same on each capacitor
How can a 1 ohm, a 2 ohm, and a 3 ohm resistor be combined?
-All three resistors in series
-All three resistors in parallel
-The 1 ohm and 2 ohm resistors in series; their combination in parallel with the 3 ohm resistor
-The 1 ohm and 3 ohm resistors in series; their combination in parallel with the 2 ohm resistor
-The 2 ohm and 3 ohm resistors in series; their combination in parallel with the 1 ohm resistor
-The 1 ohm and 2 ohm resistors in parallel; their combination in series with the 3 ohhm resistor
-The 1 ohm and 3 ohm resistors in parallel; their combination in series with the 2 ohm resistor
-The 2 ohm and 3 ohm resistors in parallel; their combination in series with the 1 ohm resistor
For a complex network of resistors in series and parallel connected to a real battery, which of the following statements is always true?
The total power dissipated by the resistors equals the power supplied by the battery
Which of the following statements must be true for any circuit?
-The current is the same everywhere
-At any junction, the total current into the junction equals the total current out of the junction
-The total change in potential around any closed path of the circuit is zero
-The direction of the current through a resistor is from high potential (+) to low potential (-)
A circuit consists of two real batteries, one with an emf of 18 V and the other with an emf of 12 V and ideal connecting wires. The positive terminals of the batteries are connected directly and their negative terminals are also connected directly. Which of the following statements are true about the batteries?
-The current is the same through both batteries
-The terminal voltage is the same for both batteries
-The terminal voltage is between 12 V and 18 V
-The 12 V battery is charging and the 18 V battery is discharging
A circuit consists of an ideal 6 V battery, a 2 ohm resistor and a 4 ohm resistor in series. How should a voltmeter be connected to measure the voltage across the 2 ohm resistor?
In parallel with the 2 ohm resistor
A circuit consists of an ideal 6 V battery, and a 2 ohm resistor, and a 4 ohm resistor in parallel. How should an ammeter be connected to measure the current through the 4 ohm resistor?
In series with the 4 ohm resistor
Which of the following statements are correct regarding an ammeter and voltmeter?
-An ammeter should have very low resistance
-A voltmeter should have very high resistance
A fully charged capacitor is connected to a resistor and a switch which is initially open. When the switch is closed...
The current decreases exponentially
Which of the following statements is true for capacitors in parallel?
The potential difference must be the same across each capacitor
Which of the following statements is true for capacitors in series?
The charge must be the same on each capacitor
What is the direction of the force on an electron moving to the right in a uniform magnetic field directed inwards?
Down
What is the direction of the force on a wire carrying a downwards current in a uniform magnetic field directed to the right?
Out
The magnetic field produced by a long, straight, current carrying wire is?
Directly proportional to the current and inversely proportional to the distance from the wire
What is the path of a charged particle with a velocity perpendicular to a magnetic field? Assume the particle remains within the field at all times. Neglect gravity and assume that the electric field is zero.
A circle whose radius is inversely proportional to the magnitude of the magnetic field
Which of the following are correct for two parallel wires carrying current in opposite directions?
-There is no magnetic field at the second wire due to the current in the first wire
-Because of that magnetic field there is a magnetic force on the second wire
-There is a magnetic field at the first wire due to the current in the second wire
-Because of that magnetic field there is a magnetic force on the first wire
-The magnetic force between the wires is repulsive
When is Ampere's law valid?
Only for situations where the current and fields are not changing in time
A flat, current carrying coil of wire is in a uniform magnetic field. When is the torque on the coil maximum?
When the plane of the coil is parallel to the magnetic field
What is the purpose of a commutator in a dc motor?
To change the direction of the current around the coil so the direction of the torque remains the same
Which of the following devices uses the principle that a current carrying coil in a magnetic field experiences a magnetic torque?
-A galvanometer
-An analog ammeter
-An ac motor
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