Physics test 2

he capacitor in the circuit shown in (Figure 1) is charged to an initial value Q. When the switch is closed, it discharges through the resistor. It takes 2.5 seconds for the charge to drop to 12Q. Part A How long does it take to drop from initial charge Q to 14Q?

t= 5s

As a proton moves through space, it creates

both an electric field and magnetic field.

If ammeters and voltmeters are not to significantly alter the quantities they are measuring,

the resistance of an ammeter should be much lower, and the resistance of a voltmeter should be much higher, than those of the circuit being measured.

A 10-V, 1.0-A dc current is run through a step-up transformer that has 10 turns on the input side and 20 turns on the output side

0 V, 0 A.

Two identical 10-V batteries and two identical 10-Ω resistors are placed in series as shown in (Figure 1)If a 10-Ω lightbulb is connected with one end connected between the batteries and other end between the resistors, how much current will flow through the lightbulb? .

0A

Which of the following statements are true about batteries?

A battery is a device that produces electricity by transforming chemical energy into electrical energy. A battery does work on electric charges to bring them to a position of higher electric potential energy so that they can flow through a circuit to a lower potential energy.

Indicate which of the following will produce a magnetic field:

A magnet. The Earth. An electric current A moving electric charge.

Which statements about the force on a charged particle placed in a magnetic field are true?

A magnetic force is exerted only if the particle is moving.

Which of the following statements are true concerning the creation of magnetic fields?

A moving electric charge creates a magnetic field at all points in the surrounding region. An electric current in a conductor creates a magnetic field at all points in the surrounding region. A permanent magnet creates a magnetic field at all points in the surrounding region.

Which of the following statements are true about ammeter and volmeters.

An ammeter is used to measure current. A voltmeter must be placed in parallel with a resistor to measure the voltage across the resistor. A voltmeter is used to measure voltage.

the figure, a conducting rod is shown moving in a uniform magnetic field . Which of the following statements are true?

An electric field is established in the rod directed from point a to point b. The magnitude of the potential difference in the rod is proportional to the velocity v of the rod. The magnitude of the potential difference in the rod is proportional to the strength of the magnetic field. The free charges in the rod are acted upon by a magnetic force.

Which of the following statements are true regarding electric generators?

An electric generator converts mechanical energy into electrical energy. An electric generator creates a time-dependent induced voltage.

Which of the following statements are true for magnetic field lines?

At every point in space, the magnetic field vector at that point is tangent to the magnetic field line through that point. Magnetic field lines can never intersect. Unlike electric field lines, magnetic field lines are continuous.

A resistor, an inductor, and a switch are all connected in series to an ideal battery of constant terminal voltage. Suppose at first the switch is open, and then, at some initial time t = 0, it is closed. Which of the following statements are true?

At the instant the switch is closed, the current begins to increase at a rate that depends upon the value of the inductance of the inductor. The steady-state value of the current depends on the resistance of the resistor.

The magnitude of the magnetic field at a certain distance from a long, straight conductor is represented by B. What is the magnitude of the magnetic field at twice the distance from the conductor?

At twice the distance, the magnitude of the field is B/2.

Which of the following statements about the force on a charged particle due to a magnetic field are not valid?

DOES NOT It depends on the particle's velocity. It depends on the particle's charge. It acts at right angles to the direction of the particle's motion. It depends on the strength of the external magnetic field

Which of the following statements are true about earth poles?

Earth's geographic north pole is actually a magnetic south pole. The south poles of two bar magnets will repel each other. The north pole of a bar magnet will attract the south pole of another bar magnet.

A 10,000-Ω resistor is placed in series with a 100-Ω resistor. The current in the 10,000-Ω resistor is 10 A. If the resistors are swapped, how much current flows through the 100-Ω resistor?

I100=10A

A proton enters a uniform magnetic field that is perpendicular to the proton's velocity (Figure 1) . What happens to the kinetic energy of the proton?

It stays the same.

A long straight wire carries a current I as shown in (Figure 1) . A small loop of wire rests in the plane of the figure. Which of the following will not induce a current in the loop?

Moving the loop in a direction parallel to the wire.

A circular loop of wire lies flat on a level table top. A bar magnet is held stationary above the circular loop with its north pole point downward. As viewed from above, in what direction does the induced current flow in the loop of wire?

No current is induced in the loop of wire.

Which of the following will not increase a generator's voltage output?

Rotating the magnetic field so that it is more closely parallel to the generator's rotation axis.

When you swipe a credit card, the machine sometimes fails to read the card. What can you do differently

Swipe the card more quickly so that the induced emf is higher.

A capacitor is connected across an AC source. Suppose the frequency of the source is doubled. What happens to the capacitive reactance of the inductor?

The capacitive reactance is reduced by a factor of 2.

A resistor and a capacitor are used in series to control the timing in the circuit of a heart pacemaker. To design a pacemaker that can double the heart rate when the patient is exercising, which statement below is true?

The capacitor needs to discharge faster, so the resistance should be decreased.

Consider two capacitors with unequal capacitance connected in series to a battery. Which of the following statements are true?

The charge stored on each of the capacitors is the same The algebraic sum of the voltages across the two capacitors is equal to the voltage supplied by the battery. The equivalent capacitance of the combination of the two capacitors is less than the capacitance of either of the capacitors.

A charged particle enters into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field vector. Ignoring the particle's weight, what type of path will the particle follow?

The charged particle will follow a circular path.

Consider three resistors with unequal resistances connected in series to a battery. Which of the following statements are true?

The current flowing through each of the resistors is the same and is equal to the current supplied by the battery. The algebraic sum of the voltages across the three resistors is equal to the voltage supplied by the battery. The equivalent resistance of the combination of resistors is greater than the resistance of any one of the three resistors.

A resistor, an inductor, and a capacitor are connected in series to an AC source. The AC source is operating at the resonance frequency. Which of the following statements are true?

The current is in phase with the driving voltage. The total voltage across the inductor and the capacitor at any instant is equal to zero.

Which of the following statements are true for magnetic force acting on a current-carrying wire in a uniform magnetic field?

The direction of the magnetic force acting on a current-carrying wire in a uniform magnetic field is perpendicular to the direction of the current. The magnetic force on the current-carrying wire is strongest when the current is perpendicular to the magnetic field lines. The direction of the magnetic force acting on a current-carrying wire in a uniform magnetic field is perpendicular to the direction of the field.

Consider a magnetic force acting on an electric charge in a uniform magnetic field. Which of the following statements are true?

The direction of the magnetic force acting on a moving electric charge in a magnetic field is perpendicular to the direction of motion. The direction of the magnetic force acting on a moving charge in a magnetic field is perpendicular to the direction of the magnetic field. A magnetic force is exerted on an electric charge moving through a uniform magnetic field. An electric charge moving perpendicular to a magnetic field experiences a magnetic force.

Consider two capacitors with unequal capacitance connected in parallel to a battery.

The equivalent capacitance of the combination is greater than the capacitance of either of the capacitors. The sum of the charge stored on each capacitor is equal to the charge supplied by the battery. The voltage across each of the capacitors is the same.

Two long parallel wires are placed side by side on a horizontal table. The wires carry equal currents in the same direction. Which of the following statements are true?

The magnetic force between the two wires is attractive. The magnetic field at a point midway between the two wires is zero.

A resistor, an inductor, and a capacitor are connected in series to an AC source. What is the phase angle between the voltages of the inductor and capacitor in this RLC circuit?

The phase angle is 180°. The phase angle is 270°.

As additional resistors are connected in series to a constant voltage source, how is the power supplied by the source affected?

The power supplied by the source decreases.

As additional resistors are connected in parallel to a constant voltage source, how is the power supplied by the source affected?

The power supplied by the source increases.

An inductor is connected in series to a fully charged capacitor. Which of the following statements are true?

The stored electric field energy can be greater than the stored magnetic field energy. . The stored electric field energy can be equal to the stored magnetic field energy. As the capacitor is discharging, the current is increasing. The stored electric field energy can be less than the stored magnetic field energy.

Why is an appliance cord with a three-prong plug safer than one with two prongs?

The third prong grounds the case, so the case cannot reach a high voltage.

wo parallel wires are vertical. The one on the left carries a 10-A current upward. The other carries 5-A current downward. Compare the magnitude of the force that each wire exerts on the other.

The two wires exert the same force on each other.

Consider three resistors with unequal resistances connected in parallel to a battery.

The voltage across each of the resistors is the same and is equal in magnitude to the voltage of the battery. The algebraic sum of the currents flowing through each of the three resistors is equal to the current supplied by the battery. The equivalent resistance of the combination of resistors is less than the resistance of any one of the three resistors.

A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. When the system reaches its steady state, what is the voltage across the resistor and the capacitor?

The voltage across the resistor is zero, and the voltage across the capacitor is equal to the terminal voltage of the battery.

A bar magnet is held above the floor and dropped (Figure 1) . In case (a), the magnet falls through a wire loop. In case (b), there is nothing between the magnet and the floor. If there is induced current, wouldnt that cost energy? Where would that energy come from in case (a)?

There is less kinetic energy in case (a) than in case (b).

Which way do the magnetic field lines produced by this wire point?

They make circles around the wire.

When a generator is used to produce electric current, the resulting electric energy originates from which source?

Whatever rotates the generator's axle.

Describe the effective capacitance when capacitors are connected in series and in parallel.

When capacitors are connected in series, the effective capacitance is less than the smallest capacitance. when capacitors are connected in parallel, the effective capacitance is greater than the largest capacitance.

As a capacitor is being charged in an RC circuit, the current flowing through the resistor is

decreasing

Which of the following statements is false? The magnetic field of a current-carrying wire

exists only if the current in the wire is changing.

A long, straight, vertical wire carries a current upward. Due east of this wire, in what direction does the magnetic field point?

north

For a charged particle, a constant magnetic field can be used to change

only the direction of the particle's velocity.

Two separate but nearby coils are mounted along the same axis. A power supply controls the flow of current in the first coil, and thus the magnetic field it produces. The second coil is connected only to an ammeter. The ammeter will indicate that a current is flowing in the second coil

only when the current in the first coil changes.

When a charged particle moves parallel to the direction of a magnetic field, the particle travels in a

straight line.

A laptop computer's charger unit converts 120 V from a wall power outlet to the lower voltage required by the laptop. Inside the charger's plastic case is a diode or rectifier that changes ac to dc plus a

transformer

A loop rests in the plane of a page of textbook while a magnetic field is directed into the page. A clockwise current is induced

when the size of the loop decreases. when the magnetic field is tilted so it is no longer perpendicular to the page.

A wire loop moves at constant velocity without rotation through a constant magnetic field. The induced current in the loop will be

zero.