PHY 112 Final

The maximum torque on a flat current-carrying loop occurs when the angle between the plane of the loop's area and the B field vector is _____ degrees: A. 0 B. 45 C. 90 D. 135

C. 90

A proton is moving to the right. Suddenly, it encounters a uniform magnetic field pointing out of the page. What direction will it go? A. Up B. Straight C. Down

C. Down

A very long straight current-carrying wire produces a magnetic field of 20mT at distance d from the wire. To measure a field of 5mT, what would d be? A. 16d B. 8d C. 4d D. 2d

D. 2d

The plates of a parallel-plate capacitor are maintained with constant voltage by a battery as they are pulled apart. During this process, the E field on the plates must

Decrease (E=v/d)

What causes an induced current?

Decreasing the area of the loop, decreasing B field, increasing B field, rotating the loop 90 degrees

T or F: A compass points north because that is the Earth's north magnetic pole.

False

T or F: Doubling the capacitance of a capacitor that is holding a constant charge causes the energy stored in that capacitor to double.

False

T or F: For AC current the RMS current, Irms is the maximum/peak current.

False

T or F: If a magnet is broken in half, one part is north and the other part is south.

False

T or F: If resistance in a constant voltage circuit is doubled, power dissipated will increase by a factor of two.

False

T or F: The eV is a unit of power.

False

T or F: The length of a wire is kept the same while its radius is doubled. The resistance doesn't change.

False

T or F: The magnitude of magnetic force that acts on a charged particle in a magnetic field is independent of charge.

False

T or F: The strength of the electric field between two oppositely charged plates is not uniform from the positive to the negative plate.

False

T or F: Two identical bulbs in series will not have the same brightness.

False

T or F: Two long parallel wires placed side-by-side on a horizontal table carry identical current straight towards you. Magnetic field exactly between the two wires points upward.

False

T or F: Two protons are released from rest, with only the electrostatic force acting, their acceleration keeps increasing.

False

T or F: We observe that a moving charged particle experiences no magnetic force. From this, we can definitely conclude that no magnetic field exists in that space

False

A charge of 12 C passes through an electroplating apparatus in 2.0 min. What is the average current in the apparatus?

0.1A 1/(2*pi*f*C)

If the length and diameter of a wire of circular cross section are both tripled, the resistance will be:

1/3 of what it originally was (R=P(L/A))

Four resistors having resistances of 20, 40, 60, and 80 ohms are connected in series across an ideal dc voltage source. If the current through this circuit is 0.5A, what is the voltage across the voltage source?

100V (V=IR)

An ideal step-up transformer doubles a primary voltage of 110V. What is the ratio of the number of turns in its primary coil to the number of turns in the secondary coil?

1:2

A series RCL circuit contains a 148 ohm resister, a 1.5uF capacitor, and a 35.7mH inductor. The frequency of the generator is 512Hz. What is the value of Xc?

207 ohms

When a dielectric material is introduced between the plates of a parallel-plate capacitor and completely fills the space, the capacitance increases by a factor of 4. What is the dielectric constant of the material that was introduced?

4 (C increase=K increase)

In a region where the E field is uniform and points in the +x direction, the electric potential is -2000V at x=8m and is +400V at x=2m. What is the magnitude of the E field?

400 V/m

An ideal parallel-plate capacitor has a capacitance of C. If the area of the plates is doubled and the distance between the plates is halved, what is the new capacitance?

4C C=Eo2A/0.5d

Two electrons are 20mm apart at the closest approach. What is the magnitude of the max E force that they exert on each other?

5.8E-25N k(q1)(q2)/d^2

A generator produces 60A of current at 120V. The voltage is usually stepped up to 4500V by a transformer and transmitted through a power line with R=1 ohm. Find the number of turns in the secondary if the primary has 200 turns.

7500 Turns

What direction does the electric field go in between 2 charged metal plates?

Positive to negative

Four unequal resistors are connected in a parallel with each other. Which one of the following statements is correct about this combination?

The equivalent resistance is less than that of the smallest resistor.

Four point charges Q of equal magnitude and sign are arranged on three of the corners of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the charge at the upper right hand corner of the square?

The lower right corner (A)

An eagle with a wingspread of 2m flies at 8m/s where the vertical component of the earth's B field is 0.2E-4T. What emf would be developed between the wings? A. 0.32mV B. 32uV C. 0V

A. 0.32mV

What size capacitor must be placed in series with a 40mH coil so the circuit will oscillate with a frequency of 1000Hz? A. 0.63uF B. 0.50uF C. 0.22uF D. 0.17uF

A. 0.63uF

What is the capacitive reactance of a circuit comprised of a 65uF capacitor and a 50Hz generator? A. 49 Ohms B. 72.5 Ohms C. 97.6 Ohms D. 145 Ohms

A. 49 Ohms

A coil lies flat on a tabletop in a region where the magnetic field vector points straight up. The magnetic field vanishes suddenly. When viewed from above, what is the sense of the induced current in this coil as the field fades? A. Clockwise B. Counterclockwise C. No induced current

A. Clockwise

An ac voltage source that has a frequency f is connected across the ends of an inductor. Which one of the following statements correctly indicates the effect on the inductive reactance when the frequency is increased to 2f? A. Inductive reactance is increased by a factor of 2 B. Inductive reactance is decreased by a factor of 2 C. IR is unchanged D. IR decreases by a factor of 2

A. Inductive reactance is increased by a factor of 2

A conducting loop of wire is placed in a magnetic field that is normal to the plane of the loop. Which one of the following actions will not result in an induced current in the loop?

A. Rotate the loop about an axis that is parallel to the field and passes through the center of the loop

T or F: A dielectric material such as paper is inserted between the plates of a capacitor as the capacitor holds a fixed charge on its plates. The electric field becomes weaker as the material is inserted.

True

T or F: A nucleus with charge +e is situated to the left of a +6 nucleus. Electrostatic force experienced by the first nucleus is to the left and is equal in magnitude to the force exerted on the other nucleus.

True

T or F: A transformer is used to increase or decrease AC current.

True

T or F: According to Lenz's Law, induced current in a circuit always opposes a change in external magnetic flux.

True

T or F: An AC voltage source that has a frequency is connected across the terminals of a capacitor. When the frequency is increased by a factor of 4, the reactance decreases by a factor of four.

True

T or F: Connecting two capacitors in parallel will allow them to store the maximum amount of energy.

True

T or F: Electrically neutral objects cannot exert an electrical force on each other.

True

T or F: If the secondary coil of a transformer contains more loops than the primary coil, then it is a step-up transformer.

True

T or F: Induced current generates its own magnetic field. This induced B field opposes change in flux.

True

T or F: It takes a large number of solar cells to produce the current needed in your home.

True

T or F: Resistivity increases as temperature goes up.

True

T or F: The amount of current in a circuit depends on the battery's emf and the resistance of the circuit.

True

T or F: The direction of a current carrying wire in a magnetic field is perpendicular to current and magnetic field.

True

T or F: The fundamental charge is equal to 1.6E-19C.

True

T or F: Transistors amplify a small voltage into a larger one.

True

T or F: Two long parallel wires are placed side-by-side on a table. If the wires carry current in the same direction, they will be attracted to each other.

True

If the maximum voltage of an AC signal is 8V, what is the rms value of this voltage? A. 2.8V B. 5.7V C. 6.2V D. 4.0V

B. 5.7V

Which one of the following statements is correct concerning the B field inside a current carrying solenoid? A. The magnetic field is zero. B. The magnetic field is non-zero and relatively uniform. C. The field is independent of windings. D. The field is independent of current.

B. The magnetic field is non-zero and relatively uniform.

Two charges of opposite sign and equal magnitude Q=0.82C are held 2m apart. Determine electric potential at P.

Zero Volts

Kirchoff's junction rule is a statement of

law of conservation of charge

Two stationary point charges q1 and q2 are shown in the figure along with a sketch of some field lines representing the electric field produced by them. What can you deduce from the sketch?

q1 is negative and q2 is positive; the magnitude of q1 is less than the magnitude of q2