Deck 20: Magnetism and Electromagnetic Waves

Question 1

The intensity of solar radiation at the top of Earth's atmosphere is 1340 W/m². A person has a projected surface area of 0.8 m². Assume that 5% of the incoming solar energy reaches Earth's surface, and that you absorb 50% of the incident energy. What amount of solar energy do you absorb in 30 minutes?

A)186 kJ
B)257 kJ
C)540 kJ
D)641 kJ

Answer 1

540 kJ

Question 2

An electron is accelerated through 1500 V from rest, and then enters a uniform 2.00 T magnetic field. What is the maximum value of the magnetic force this charge can experience?

A)7.12 × 10^-14 N
B)3.67 × 10^-12 N
C)7.35 × 10^-12 N
D)6.67 × 10^-11 N

Answer 2

7.35 × 10^-12 N

Question 3

Niobium metal becomes a superconductor when cooled below 9 K. Its superconductivity is destroyed when the surface magnetic field exceeds 0.100 T. What is the maximum current that a 1.50 mm diameter niobium wire can carry and remain superconducting in the absence of any external magnetic field?

A)113 A
B)225 A
C)375 A
D)425 A

Answer 3

375 A

Question 4

An electron moving freely in a circular path perpendicular to a constant magnetic field takes 2.50 ns to complete one revolution. What is the magnitude of the magnetic field?

A)6.33 mT
B)9.56 mT
C)10.56 mT
D)12.04 mT

Question 5

A Wien filter (velocity selector) consists of uniform electric and magnetic fields, with E pointing along the z-axis and B along the y-axis. B has a value of 15.0 mT. What is the value of E such that a 600 eV electron moving along the positive x-axis is undeflected?

A)8.9 × 10⁴ N/C
B)2.2 × 10⁵ N/C
C)5.3 × 10⁵ N/C
D)1.9 × 10⁶ N/C

Question 6

A singly charged positive ion has a mass of 3.20 × 10^-26 kg. After being accelerated from rest through a potential difference of 875 V, the ion enters a magnetic field of 0.42 T along a direction perpendicular to the direction of the field. What is the radius of the path of the ion in the field?

A)2.23 cm
B)2.40 cm
C)4.45 cm
D)8.74 cm

Question 7

A coil of 100 turns and radius 15.0 cm surrounds a long solenoid of radius 2.5 cm and 2000 turns/metre. The current in the solenoid changes as I = (10.0 A)sin(377t). What is the maximum value of the induced electric field in the 100 turn coil?

A)15.4 mV/m
B)19.7 mV/m
C)22.4 mV/m
D)25.4 mV/m

Question 8

A lightning bolt may carry a current of 1.50 × 10⁴ A for a short period of time. Supposing that the bolt extends far above and below the point of observation, what is the resulting magnetic field 100 m from the bolt?

A)15 ìT
B)30 ìT
C)45 ìT
D)60 ìT

Question 9

The Cosmic Microwave Background is blackbody radiation with a temperature of 2.70 K. What is the energy of the photons (in electron volts) corresponding to the maximum intensity?

A)1.2 eV
B)6.01 × 10^-3 eV
C)1.2 × 10^-3 eV
D)6.0 × 10^-4 eV

Question 10

A particle (q = 2.0 ìC, m = 5.0 mg) moves in a uniform magnetic field with a velocity of magnitude 2.5 km/s and a direction that is 60° away from that of the magnetic field. The particle is observed to have an acceleration with a magnitude of 5.1 m/s². What is the magnitude of the magnetic field?

A)2.1 T
B)3.0 T
C)5.9 T
D)7.3 T

Question 11

Consider an electron near Earth's equator. In which direction does it tend to deflect if its velocity is directed downward?

A)north
B)west
C)east
D)south

Question 12

The south pole of a magnet is thrust into a loop of wire, causing an induced electric field E in the wire. In which direction relative to the wire does E point?

A)radially outward from the centre of the loop
B)clockwise, as seen from the side of the magnet
C)counterclockwise, as seen from the side of the magnet
D)radially inward from the centre of the loop

Question 13

A flat circular loop of wire consists of a single turn with a radius of 2.5 cm, and is perpendicular to a magnetic field that increases uniformly in magnitude from 0.80 T to 2.50 T in 0.50 s. What is the resulting induced current if the loop has a resistance of 2.00 Ù?

A)1.22 mA
B)3.34 mA
C)6.25 mA
D)8.74 mA

Question 14

A person with skin temperature of 37.00°C is in a room when the temperature of the room is (i) 30.00°C and then (ii) 15.00°C. What is the ratio (ii):(i) of heat loss from the person's body, assuming the emissivity remains constant?

A)3.23
B)2.92
C)2.41
D)1.56

Question 15

Two long, parallel wires are attracted to each other by a force per unit length of 160 ìN/m when they are separated by a vertical distance of 0.50 m. The current in the upper wire is 20.0 A to the right. Where on the line in the plane of the two wires does the total magnetic field equal zero?

A)0.1 m below the upper wire
B)0.2 m below the upper wire
C)halfway between the wires
D)0.3 m below the upper wire

Question 16

A circular-plate capacitor with a radius of 6 cm and plate separation of 1.5 mm is being charged from a battery. At a particular instant, the charging current is 1 ìC/s. At that instant, what is the strength of the induced magnetic field 3 cm from the centre of the plates?

A)1.6 × 10^-11 T
B)2.8 × 10^-12 T
C)1.7 × 10^-12 T
D)2.5 × 10^-13 T

Question 17

A strong electromagnet produces a uniform magnetic field of 0.50 T over a circular cross-section of radius 25 cm. A circular coil with 100 turns and a total resistance of 40.00 Ù is placed around the electromagnet. The current is smoothly reduced in the electromagnet until it reaches zero in 50.00 ms. What is the current induced in the coil?

A)0.41 A
B)0.78 A
C)0.81 A
D)1.56 A

Question 18

A straight wire 80 cm long carries a current of 20 A, and makes an angle of 45° with a uniform magnetic field. If the force on the wire is 1.20 N, what is the magnitude of B?

A)0.08 T
B)0.11 T
C)0.52 T
D)2.21 T

Question 19

Under which of these circumstances will the magnetic flux through a loop perpendicular to a uniform magnetic field change?

A)if the loop is replaced by two loops, each of which has half the area of the original loop
B)if the loop moves at constant velocity while remaining perpendicular to and within the uniform magnetic field
C)if the loop is rotated through 180 degrees about an axis through its centre and in the plane of the loop
D)if the loop moves at constant velocity in a direction parallel to the axis of the loop while remaining in the uniform magnetic field

Question 20

An electron moving along the positive x-axis perpendicular to a magnetic field experiences a magnetic deflection in the negative y-direction. What is the direction of the magnetic field?

A)-z-direction
B)+z-direction
C)-y-direction
D)+y-direction

Question 21

The induced electric field in a region of time-varying magnetic field does NOT depend on the source of the variation, such as a moving magnet or a variable current in an electromagnet, but only on the rate of variation of the flux through the region.

Question 22

The value of the loop integration in Ampère's law does NOT depend on the shape of the loop, but only on the amount of current it encloses.

Question 23

Two particles are ejected horizontally into a region of vertical magnetic field, and are deflected in opposite directions in the horizontal plane. The particle deflected to the right has positive charge; the one deflected to the left has negative charge.

Question 24

An electric field exerts a force on a stationary charged object.

Question 25

In Aston's mass spectrometer, the ions strike the plate in order of their masses.

Question 26

Charged particles from outer space (solar wind, cosmic rays) strike Earth more frequently near the poles than near the equator. Why?

Question 27

A charged particle is injected into a uniform magnetic field at right angles to the field. Show that it executes circular motion around the magnetic field direction, with an orbital period that is independent of the velocity with which it was injected.

Question 28

Do Maxwell's equations allow for the existence of magnetic monopoles? Explain.

Question 29

The electrons in a cathode ray tube may be directed to hit the fluorescent screen at any desired point. Discuss briefly how this may be accomplished using electric and magnetic fields.

Question 30

Suppose a conducting metal bar moves horizontally, at right angles to its length, through a vertical magnetic field. Describe what effect you would expect.

Question 31

By considering the parallel plate capacitor that is being charged, show that the "displacement current"-defined as å₀ times the first integral on the right-hand side of the last equation in Eq. [20.24]-is equal to the "conduction current," I, in the same equation.

Question 32

In what ways would an infrared photograph of a person look different from one taken with visible light?

Question 33

A conducting ribbon carrying an electric current is placed in a magnetic field with its face and the direction of current both at right angles to the field. Describe what you expect to happen to the charge carriers in the wire. What effect would this have, and how would you measure it?

Question 34

Explain why a charged particle passing through a stationary magnetic field does NOT change its kinetic energy.

Question 35

The electric and magnetic fields of an electromagnetic wave propagating in a vacuum are in phase with each other.

Question 36

When an electromagnetic wave passes from one medium to another, the velocity remains the same.

Question 37

A current-carrying rectangular loop of wire is mounted on an axis parallel to two opposite sides and mid-way between them. The loop is placed in a uniform magnetic field so that the field is parallel to the plane of the loop and perpendicular to the axis on which the loop is mounted. What happens to the loop?

Question 38

Magnetic fields may be produced by moving charges, electric currents, and changing electric fields.

Question 39

A magnetic field always exerts a force on a moving charge.

Question 40

If the number of turns of a solenoid is doubled, the strength of the magnetic field (for a fixed current) doubles.