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Question 1Electricity Magnetism
A 6.0 ohm resistor is connected to a 12 V battery. What current flows through the resistor?
- 0.50 A
- 1.0 A
- 2.0 A Correct answer.
- 72 A
Explanation
Ohm's law gives I = V / R = 12 V / 6.0 ohm = 2.0 A.
Question 2Electricity Magnetism
Two identical 6.0 ohm resistors are connected in parallel. What is their equivalent resistance?
- 12.0 ohm
- 6.0 ohm
- 1.5 ohm
- 3.0 ohm Correct answer.
Explanation
For two identical resistors in parallel, the equivalent resistance is half of one resistor: 6.0 ohm / 2 = 3.0 ohm.
Question 3Electricity Magnetism
In a uniform electric field pointing to the right, what is the direction of the force on a positive test charge?
- To the left
- To the right Correct answer.
- Perpendicular to the field
- No force acts
Explanation
The electric field direction is defined as the direction of the force on a positive test charge, so the force is to the right.
Question 4Electricity Magnetism
An electron enters a uniform magnetic field with its velocity perpendicular to the field. Ignoring other forces, what path does it follow?
- A straight line at constant speed
- A parabola
- A circular path Correct answer.
- A path parallel to the field lines
Explanation
With velocity perpendicular to a uniform magnetic field, the magnetic Lorentz force is always perpendicular to the velocity and acts as a centripetal force, producing circular motion.
Question 5Electricity Magnetism
If the plate separation of an ideal parallel-plate capacitor is increased while plate area and dielectric stay the same, what happens to its capacitance?
- It decreases Correct answer.
- It increases
- It stays exactly the same
- It becomes zero immediately
Explanation
For a parallel-plate capacitor, C is proportional to A / d. Increasing the separation d decreases the capacitance.
Question 6Electricity Magnetism
Which situation can induce a voltage in a coil according to Faraday's law?
- A constant magnetic flux through the coil
- A changing magnetic flux through the coil Correct answer.
- A coil at rest far from all magnets
- A resistor connected to an uncharged capacitor
Explanation
Faraday's law states that an induced voltage occurs when the magnetic flux through a circuit changes with time.
Question 7Electricity Magnetism
What is the SI unit of magnetic flux density B?
- tesla Correct answer.
- coulomb
- weber
- volt
Explanation
Magnetic flux density B is measured in tesla. Magnetic flux itself is measured in weber.
Question 8Electricity Magnetism
A 200 microF capacitor is charged to 10 V. What charge is stored on one plate?
- 2.0 C
- 0.020 C
- 0.0020 C Correct answer.
- 5.0 x 10^-5 C
Explanation
Charge is Q = C V = 200 x 10^-6 F x 10 V = 2.0 x 10^-3 C.
Question 9Electricity Magnetism
Two parallel plates have a potential difference of 600 V and separation 0.030 m. What is the magnitude of the uniform electric field between them?
- 20000 V/m Correct answer.
- 180 V/m
- 20 V/m
- 0.000050 V/m
Explanation
For a uniform field between plates, E = U / d = 600 V / 0.030 m = 20000 V/m.
Question 10Electricity Magnetism
A charge of 2.0 microC is placed in an electric field of 3.0 x 10^4 N/C. What force acts on it?
- 6.0 x 10^10 N
- 1.5 x 10^10 N
- 0.015 N
- 0.060 N Correct answer.
Explanation
Electric force is F = q E = 2.0 x 10^-6 C x 3.0 x 10^4 N/C = 6.0 x 10^-2 N.
Question 11Electricity Magnetism
A proton is accelerated from rest through a potential difference of 500 V. What kinetic energy does it gain?
- 500 J
- 500 eV Correct answer.
- 250 eV
- 0 eV
Explanation
A particle with charge +e gains kinetic energy q U = e x 500 V = 500 eV.
Question 12Electricity Magnetism
A singly charged ion with charge 1.6 x 10^-19 C moves at 2.0 x 10^6 m/s perpendicular to a 0.50 T magnetic field. What is the magnetic force?
- 6.4 x 10^-26 N
- 1.6 x 10^-19 N
- 1.6 x 10^-13 N Correct answer.
- 4.0 x 10^6 N
Explanation
For perpendicular motion, F = q v B = 1.6 x 10^-19 x 2.0 x 10^6 x 0.50 = 1.6 x 10^-13 N.
Question 13Electricity Magnetism
A 100-turn coil has its magnetic flux per turn reduced uniformly from 0.020 Wb to 0 in 0.10 s. What is the magnitude of the induced emf?
- 20 V Correct answer.
- 2.0 V
- 0.020 V
- 2000 V
Explanation
Faraday's law gives |emf| = N |Delta Phi| / Delta t = 100 x 0.020 / 0.10 = 20 V.
Question 14Electricity Magnetism
What does Lenz's law state about an induced current?
- It always flows clockwise
- It always increases the original flux change
- It exists only in superconductors
- It acts to oppose the change in magnetic flux that produced it Correct answer.
Explanation
Lenz's law gives the direction of induced current: its magnetic effect opposes the change in flux that caused the induction.
Question 15Electricity Magnetism
A resistor of 10 kOhm is connected in series with a 100 microF capacitor. What is the RC time constant?
- 0.001 s
- 1.0 s Correct answer.
- 100 s
- 1000 s
Explanation
The time constant is tau = R C = 10000 ohm x 100 x 10^-6 F = 1.0 s.
Question 16Electricity Magnetism
A 100 microF capacitor is charged to 20 V. Approximately how much energy is stored in it?
- 2.0 J
- 0.20 J
- 0.020 J Correct answer.
- 200 J
Explanation
Capacitor energy is E = 0.5 C V^2 = 0.5 x 100 x 10^-6 x 20^2 = 0.020 J.
Question 17Electricity Magnetism
In an ideal LC circuit, what happens to the energy during an oscillation?
- It is continuously lost as heat
- It transfers between the capacitor's electric field and the inductor's magnetic field Correct answer.
- It remains only in the resistor
- It becomes gravitational potential energy
Explanation
In an ideal LC oscillator, energy alternates between electric-field energy in the capacitor and magnetic-field energy in the inductor.
Question 18Electricity Magnetism
An ideal transformer has 200 primary turns and 50 secondary turns. If the primary voltage is 12 V, what is the secondary voltage?
- 48 V
- 12 V
- 3.0 V Correct answer.
- 0.25 V
Explanation
For an ideal transformer, V_s / V_p = N_s / N_p = 50 / 200 = 0.25. Therefore V_s = 0.25 x 12 V = 3.0 V.
Question 19Electricity Magnetism
Why is electrical power transmitted over long distances at high voltage?
- For a given power, high voltage allows lower current and reduces I^2 R losses Correct answer.
- High voltage makes wire resistance exactly zero
- High voltage eliminates the need for transformers
- High voltage changes alternating current into direct current
Explanation
For fixed power P = U I, increasing voltage lowers current. Since heating loss is I^2 R, lower current greatly reduces transmission losses.
Question 20Electricity Magnetism
In a velocity selector, crossed fields have E = 2.0 x 10^4 V/m and B = 0.10 T. What speed passes undeflected?
- 2.0 x 10^3 m/s
- 2.0 x 10^4 m/s
- 5.0 x 10^-6 m/s
- 2.0 x 10^5 m/s Correct answer.
Explanation
Undeflected motion requires electric and magnetic forces to balance: q E = q v B, so v = E / B = 2.0 x 10^4 / 0.10 = 2.0 x 10^5 m/s.
Question 21Electricity Magnetism
What causes the Hall voltage in a current-carrying conductor placed in a magnetic field?
- Heating of the conductor by radiation
- Charge separation due to the magnetic Lorentz force Correct answer.
- Direct conversion of mass into charge
- The disappearance of all mobile charge carriers
Explanation
Moving charge carriers experience a magnetic Lorentz force, separating charge across the conductor until an electric Hall field balances the magnetic force.
Question 22Electricity Magnetism
A flat loop is perpendicular to a uniform magnetic field. If the loop area is doubled while B stays constant, what happens to the magnetic flux?
- It halves
- It stays the same
- It doubles Correct answer.
- It becomes zero
Explanation
For a loop perpendicular to the field, magnetic flux is Phi = B A. Doubling A doubles Phi when B is constant.
Question 23Electricity Magnetism
In an ideal LC oscillator, the period is proportional to sqrt(L C). If the capacitance is made four times larger and L is unchanged, what happens to the period?
- It doubles Correct answer.
- It halves
- It becomes four times larger
- It is unchanged
Explanation
Since T is proportional to sqrt(C), increasing capacitance by a factor of 4 increases the period by sqrt(4) = 2.
Question 24Electricity Magnetism
Two identical positive point charges are fixed at equal distances on opposite sides of point P. What are the net electric field and net electric potential at P?
- Field is zero; potential is positive Correct answer.
- Field is positive; potential is zero
- Field and potential are both zero
- Field is zero; potential is negative
Explanation
The electric field vectors from the two identical charges cancel at P because they point in opposite directions. Electric potential is a scalar and adds, so the net potential is positive.
Question 25Electricity Magnetism
A parallel-plate capacitor is charged and then disconnected from the battery. The plate separation is doubled. What happens to the capacitor voltage and stored energy?
- Voltage halves and energy halves
- Voltage doubles and energy doubles Correct answer.
- Voltage stays constant and energy halves
- Voltage doubles and energy stays constant
Explanation
After disconnection, charge Q stays constant. Doubling plate separation halves capacitance. Since V = Q/C and E = Q^2/(2C), both voltage and stored energy double.
Question 26Electricity Magnetism
A proton and an electron enter the same uniform magnetic field with the same speed perpendicular to the field. Which particle has the larger circular path radius?
- The electron, because it has negative charge
- The proton, because it has much larger mass Correct answer.
- They have equal radii because charge magnitudes are equal
- Neither moves in a circle
Explanation
For perpendicular motion, r = m v / (|q| B). The proton and electron have equal charge magnitude and speed, but the proton's much larger mass gives a much larger radius.
Question 27Electricity Magnetism
Two singly charged positive ions are accelerated through the same voltage and then enter the same magnetic field perpendicular to their velocity. Ion B has four times the mass of ion A. How do their path radii compare?
- Ion B has one fourth the radius of ion A
- Ion B has the same radius as ion A
- Ion B has twice the radius of ion A Correct answer.
- Ion B has four times the radius of ion A
Explanation
After acceleration through voltage U, v = sqrt(2 q U / m). In the magnetic field, r = m v /(q B) = sqrt(2 m U / q)/B, so r is proportional to sqrt(m). Four times the mass gives twice the radius.
Question 28Electricity Magnetism
The magnetic flux through a single loop rises uniformly from 0 to 0.30 Wb in 0.10 s, stays constant for 0.10 s, then falls uniformly to 0 in 0.30 s. Which induced-emf description is correct?
- 3.0 V, then 3.0 V, then 3.0 V all with the same sign
- 0 V, then 3.0 V, then 1.0 V with the same sign
- 3.0 V, then 0 V, then 3.0 V with the same sign
- 3.0 V, then 0 V, then 1.0 V with opposite sign during the fall Correct answer.
Explanation
The emf magnitude is |Delta Phi / Delta t|. The rise gives 0.30/0.10 = 3.0 V; constant flux gives 0 V; the fall gives 0.30/0.30 = 1.0 V with opposite sign because the flux change reverses direction.
Question 29Electricity Magnetism
A charged capacitor discharges through a resistor. After one RC time constant, approximately what fraction of the initial voltage remains?
- 0
- 0.25
- 0.37 Correct answer.
- 0.63
Explanation
For capacitor discharge, V(t) = V0 e^(-t/RC). At t = RC, V = V0/e, which is about 0.37 V0.
Question 30Waves Optics
A wave has frequency 2.0 Hz and wavelength 3.0 m. What is its wave speed?
- 1.5 m/s
- 2.0 m/s
- 3.0 m/s
- 6.0 m/s Correct answer.
Explanation
Wave speed is v = f lambda = 2.0 Hz x 3.0 m = 6.0 m/s.
Question 31Waves Optics
An alternating signal has a period of 0.020 s. What is its frequency?
- 50 Hz Correct answer.
- 0.020 Hz
- 20 Hz
- 500 Hz
Explanation
Frequency is the reciprocal of period: f = 1 / T = 1 / 0.020 s = 50 Hz.
Question 32Waves Optics
Which statement correctly describes sound waves in air?
- They are transverse electromagnetic waves
- They can travel through a vacuum
- They are longitudinal mechanical waves Correct answer.
- They require no medium
Explanation
Sound in air is a longitudinal mechanical wave: pressure variations propagate through a material medium.
Question 33Waves Optics
What happens to parallel light rays that enter an ideal converging lens parallel to its principal axis?
- They spread as if from the focal point
- They reflect back along the same path
- They are absorbed by the lens
- They meet at the focal point Correct answer.
Explanation
An ideal converging lens refracts rays parallel to the principal axis so that they pass through the focal point on the far side.
Question 34Waves Optics
For two coherent light waves, a bright interference maximum occurs when their path difference is:
- One half-wavelength
- An integer multiple of the wavelength Correct answer.
- Any nonzero distance
- Exactly one quarter-wavelength
Explanation
Constructive interference occurs when the path difference is m lambda, where m is an integer, so the waves arrive in phase.
Question 35Waves Optics
A light ray enters glass from air and slows down. If it enters at an angle to the normal, how does it bend?
- Away from the normal
- Toward the normal Correct answer.
- It does not change direction
- It reverses direction completely
Explanation
When light enters a medium where its speed is lower and the refractive index is higher, it bends toward the normal.
Question 36Waves Optics
For a small-angle pendulum, what happens to the period if the length is made four times larger?
- It becomes four times larger
- It becomes one fourth as large
- It is unchanged
- It becomes two times larger Correct answer.
Explanation
For a simple pendulum, T = 2 pi sqrt(L / g). Quadrupling L multiplies the period by sqrt(4) = 2.
Question 37Waves Optics
A string of length 1.0 m is fixed at both ends and vibrates in its fundamental mode. What is the wavelength of the standing wave?
- 2.0 m Correct answer.
- 1.0 m
- 0.50 m
- 4.0 m
Explanation
For a string fixed at both ends in the fundamental mode, the length is half a wavelength, so lambda = 2 L = 2.0 m.
Question 38Waves Optics
In a double-slit experiment, what happens to the fringe spacing on the screen if the wavelength of the light is increased while slit separation and screen distance stay fixed?
- It becomes zero
- It decreases
- It stays the same
- It increases Correct answer.
Explanation
Fringe spacing is approximately Delta y = lambda L / d. Increasing lambda increases the fringe spacing when L and d stay fixed.
Question 39Waves Optics
Diffraction is most noticeable when an opening or obstacle is:
- Much larger than the wavelength
- Comparable in size to the wavelength Correct answer.
- At absolute zero
- Made only of magnetic material
Explanation
Diffraction becomes especially noticeable when the aperture or obstacle size is of the same order as the wavelength.
Question 40Waves Optics
An object is 30 cm from a converging lens with focal length 10 cm. Where is the real image formed?
- 7.5 cm from the lens
- 10 cm from the lens
- 15 cm from the lens Correct answer.
- 30 cm from the lens
Explanation
Using 1/f = 1/u + 1/v gives 1/v = 1/10 - 1/30 = 2/30 = 1/15, so v = 15 cm.
Question 41Waves Optics
Total internal reflection can occur only when light travels:
- From a higher refractive index medium toward a lower refractive index medium at an angle above the critical angle Correct answer.
- From vacuum into glass at any angle
- Perpendicular to a boundary between identical media
- Through a lens with no refraction
Explanation
Total internal reflection requires travel from higher to lower refractive index and an incidence angle greater than the critical angle.
Question 42Waves Optics
A sound source moves toward a stationary observer. Compared with the emitted frequency, the observed frequency is:
- Zero
- Lower
- Unchanged
- Higher Correct answer.
Explanation
When a source moves toward an observer, wavefronts arrive closer together, so the observed frequency is higher than the emitted frequency.
Question 43Waves Optics
Which type of electromagnetic radiation has a higher frequency than visible violet light?
- Radio waves
- Ultraviolet radiation Correct answer.
- Microwaves
- Infrared radiation
Explanation
Ultraviolet radiation lies just beyond violet in the electromagnetic spectrum and has higher frequency than visible light.
Question 44Waves Optics
A driven oscillator shows resonance when the driving frequency is:
- Exactly zero
- Much smaller than any natural frequency
- Randomly varied each cycle
- Close to the oscillator's natural frequency Correct answer.
Explanation
Resonance occurs when the driving frequency is close to the natural frequency, allowing efficient energy transfer and large amplitude.
Question 45Waves Optics
The polarization of light is strong evidence that light waves are:
- Longitudinal only
- Transverse Correct answer.
- Mechanical sound waves
- Unable to interfere
Explanation
Only transverse waves can show polarization in the usual sense, so light polarization demonstrates transverse electromagnetic wave behavior.
Question 46Waves Optics
A diffraction grating is used with red and blue light in the same order. Which color is diffracted to the larger angle?
- Red light, because it has the longer wavelength Correct answer.
- Blue light, because it has the shorter wavelength
- Both at the same angle
- Neither, because gratings work only for radio waves
Explanation
For a grating, m lambda = d sin theta. In the same order, the longer wavelength red light gives a larger sin theta and therefore a larger angle.
Question 47Waves Optics
In a damped oscillator, the amplitude is observed to halve every 5.0 s. Since mechanical energy is proportional to amplitude squared, what fraction of the original energy remains after 5.0 s?
- 1/4 Correct answer.
- 1/2
- 1/sqrt(2)
- 1/8
Explanation
If amplitude becomes A/2, energy proportional to A^2 becomes (A/2)^2 / A^2 = 1/4 of the original energy.
Question 48Waves Optics
An air column closed at one end and open at the other has length 0.85 m. Using sound speed 340 m/s, what is its fundamental frequency?
- 50 Hz
- 200 Hz
- 400 Hz
- 100 Hz Correct answer.
Explanation
For a closed-open pipe in the fundamental mode, L = lambda/4, so lambda = 4L = 3.4 m. Then f = v/lambda = 340/3.4 = 100 Hz.
Question 49Waves Optics
In a double-slit experiment, slit separation is 0.50 mm, screen distance is 2.0 m, and wavelength is 500 nm. What is the approximate fringe spacing?
- 0.20 mm
- 2.0 mm Correct answer.
- 20 mm
- 0.50 mm
Explanation
Fringe spacing is Delta y = lambda L / d = (5.00 x 10^-7 m x 2.0 m) / (5.00 x 10^-4 m) = 2.0 x 10^-3 m = 2.0 mm.
Question 50Waves Optics
Monochromatic light of wavelength 600 nm passes through a single slit of width 0.20 mm. What is the approximate angle of the first minimum in radians?
- 3.0 rad
- 0.30 rad
- 3.0 x 10^-3 rad Correct answer.
- 1.2 x 10^-10 rad
Explanation
For the first single-slit minimum, sin theta = lambda/a. With small angles, theta = 600 x 10^-9 / 0.20 x 10^-3 = 3.0 x 10^-3 rad.