Physics test 2 MC

A circular coil of 20 turns and radius 5.0 cm is placed with its plane oriented at 90° to a uniform magnetic field of 0.10 T. The field is now increased at a steady rate, reaching a value of 0.50 T after 4.0 seconds. What magnitude of emf is induced in the coil? A) 0.016 V B) 0.021 V C) 0.026 V D) 0.031 V E) 0.036 V

A) 0.016 V

A straight wire carries a current of 10 A at an angle of 30° with respect to the direction of a uniform 0.30-T magnetic field. Find the magnitude of the magnetic force on a 0.50-m length of the wire. A) 0.75 N B) 1.5 N C) 3.0 N D) 6.0 N

A) 0.75 N (F=ILBsin(theta))

A 7.0-Ω resistor is connected across the terminals of a battery having an internal emf of 10 V. If 0.50-A current flows, what is the internal resistance of the battery? A) 13 Ω B) 20 Ω C) 10.8 Ω D) 27.0 Ω

A) 13 Ω (emf/i)- r

A 5.0-μF and a 12.0-μF capacitor are connected in series, and the series arrangement is connected in parallel to a capacitor. How much capacitance would a single capacitor need to replace this combination of three capacitors? of three capacitors? A) 33 μF B) 13 μF C) 16 μF D) 38 μF

A) 33 μF

As shown in the figure, a wire and a 10-Ω resistor are used to form a circuit in the shape of a square with dimensions 20 cm by 20 cm. A uniform but non-steady magnetic field is directed into the plane of the circuit. The magnitude of the magnetic field is steadily decreased from 2.70 T to 0.90 T in a time interval of 96 ms. What is the induced current in the circuit, and what is its direction through the resistor? A) 75 mA, from b to a B) 45 mA, from b to a C) 75 mA, from a to b D) 45 mA, from a to b E) 110 mA, from a to b

A) 75 mA, from b to a (emf=BAsintheta) (then Emf/r)

Three identical capacitors are connected in series across a potential source (battery). If a charge of Q flows into this combination of capacitors, how much charge does each capacitor carry? A) 3Q B) Q C) Q/3 D) Q/9

B) Q

***REPEAT***A circular coil of copper wire is lying flat on a horizontal table. A bar magnet is held above the center of the coil with its south pole downward. The magnet is released from rest and falls toward the coil. As viewed from above, what is the direction of the current induced in the coil as the magnet approaches the coil? A) counterclockwise B) clockwise C) No current is induced in the coil. D) An emf but no current is induced in the coil.

B) clockwise

An ideal ammeter should A) have a high coil resistance. B) introduce a very small series resistance into the circuit whose current is to be measured. C) introduce a very large series resistance into the circuit whose current is to be measured. D) consist of a galvanometer in series with a large resistor.

B) introduce a very small series resistance into the circuit whose current is to be measured.

An electron moves with a speed of 8.0 × 106 m/s along the +x-axis. It enters a region where there is a magnetic field of 2.5 T, directed at an angle of 60° to the +x-axis and lying in the xy-plane. Calculate the magnitude of the magnetic force on the electron. (e = 1.60 × 10-19 C) A) 2.8 × 10-10 N B) 3.2 × 10-10 N C) 2.8 × 10-12 N D) 3.2 × 10-12 N E) 0 N

C) 2.8 × 10-12 N (F=qvbsin(theta))

A high power line carries a current of 1.0 kA. What is the strength of the magnetic field this line produces at the ground, 10 m away? (μ0 = 4π × 10-7 T ∙ m/A) A) 4.7 μT B) 6.4 μT C) 20 μT D) 56 μT

C) 20 μT (B=μ0*I/2PIR)

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the length of the solenoid becomes twice as long (to 2L), but all other quantities (N and b) remained the same, the magnetic field inside the solenoid will A) remain the same. B) become twice as strong as initially. C) become one-half as strong as initially. D) become four times as strong as initially. E) become one-fourth as strong as initially.

C) become one-half as strong as initially. (solenoid equation)

**REPEAT**A wire is carrying current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field? A) horizontally towards the north B) horizontally towards the south C) horizontally towards the east D) horizontally towards the west E) vertically upward

C) horizontally towards the east

When unequal resistors are connected in series across an ideal battery, A) the same power is dissipated in each one. B) the potential difference across each is the same. C) the current flowing in each is the same. D) the equivalent resistance of the circuit is less than that of the smallest resistor. E) the equivalent resistance of the circuit is equal to the average of all the resistances.

C) the current flowing in each is the same.

Two long, parallel wires carry currents of different magnitudes. If the amount of current in one of the wires is doubled, what happens to the magnitude of the force that each wire exerts on the other? A) It is increased by a factor of 8. B) It is increased by a factor of 4. C) It is increased by a factor of 3. D) It is increased by a factor of 2. E) It is increased by a factor of √2.

D) It is increased by a factor of 2.

The wire in the figure carries a current I that is increasing with time at a constant rate. The wire and the three loops are all in the same plane. What is true about the currents induced in each of the three loops shown? A) No current is induced in any loop. B) The currents are counterclockwise in all three loops. C) The currents are clockwise in all three loops. D) Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current. E) Loop A has counterclockwise current, loop B has no induced current, and loop C has clockwise current.

D) Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current.

Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in opposite directions, A) one wire is lifted slightly while the other wire is forced downward against the table's surface. B) both wires are lifted slightly. C) the wires pull toward each other. D) the wires push away from each other.

D) the wires push away from each other.

In a certain velocity selector consisting of perpendicular electric and magnetic fields, the charged particles move toward the east, and the magnetic field is directed to the north. What direction should the electric field point? A) toward the east B) toward the west C) toward the south D) vertically upward E) vertically downward

E) vertically downward

An electron moving toward north, at right angles to a magnetic field, experiences a magnetic force toward west. The direction of the magnetic field is toward (note the diagram on the cover page) A) west. B) east. C) north. D) vertically downward. E) vertically upward.

E) vertically upward.