Physics q bank - multiple choice

60 million nuclei of radioactive americium 241 (half-life 430 years).

When fewer than 3.75 × 10⁶ americium nuclei remain, the ionization smoke detector will not operate due to insufficient ionization. How much time will pass before there are this many nuclei remaining?

1720 years

The explanation for the fact that radioactive isotopes of an element exhibit the same chemical behavior as the stable isotopes of the element is that each has the same:

atomic number

wavelength of 6.0 × 10^–7 m and has an intensity of 1.0 × 10^–3 W. The speed of light in air is 3.0 × 10⁸ m/s.

The frequency of the light used in photodiode detectors is:

5 × 10^14 Hz.

Destructive interference occurs in photodiode detectors when direct and scattered light rays take paths to the photocell that differ in phase by:

180 degrees

The light beam usually has a wavelength of 6.0 × 10^–7 m

The speed of light in air is 3.0 × 10⁸ m/s.

Advanced photodiode detectors have a second light-emitting diode, operating at a wavelength of 2.0 × 10^–7 m, to detect even smaller smoke particles from smoldering flames. What is the frequency difference between the two light beams?

1.0 × 10^15 Hz

separated by 3 cm with a 5-V potential difference across them

What is the magnitude of the electric field between the two electrodes in ionization type detectors?

166 N/C

Which of the waveforms shown in Figure 1 has the shortest period?

same as the period of the first harmonic.

At the second position where the three curves intersect in Figure 1a, the curves are all:

at zero displacement

If the frequency of the first harmonic in Figure 2a is 100 Hz, what is the period of the second harmonic?

.005 sec

A stationary receiver detects a change in frequency of the signal from a jet flying directly away from it at 300 m/s. Which of the following receivers will detect the same change in frequency from a jet moving away at 600 m/s?

A receiver moving at 300 m/s in the same direction as the jet

Why are the percentages of the change in frequency and wavelength much greater when sound waves are used instead of radio waves in these experiments?

Sound waves travel more slowly.

A receiver is in a jet flying alongside another jet that is emitting 2.0 x 10⁶ Hz radio waves. If the jets fly at 268 m/s, what is the change in frequency detected at the receiver?

0 Hz

An astronaut on Earth notes that in her soft drink an ice cube floats with 9/10 of its volume submerged. If she were instead in a lunar module parked on the Moon where the gravitation force is 1/6 that of Earth, the ice in the same soft drink would float:

with 9/10 submerged.

A beam of light shines into a transparent medium with parallel surfaces. Part of the beam is reflected back into the air as diagrammed above. The index of refraction of the medium is 1.5. Which of the following is true?

θ = θ′ and θ > α

A student has a thin copper beaker containing 100 g of a pure metal in the solid state. The metal is at 215°C, its exact melting temperature. If the student lights a Bunsen burner and holds it for a fraction of a second under the beaker, what will happen to the metal?

A small amount of the metal will turn to liquid, with the temperature remaining the same.

Which of the following best describes the movement of an electron after it is ejected from the cathode?

It accelerates toward the anode.

If the speed of the charged particle described in the passage is increased by a factor of 2, the electrical force on the particle will:

remain the same

If a dielectric is added between the plates:

increase

Making which of the following changes to a circuit element will increase the capacitance of the capacitor described in the passage?

Increasing the area of the capacitor plates

A charged particle with a mass of m and a charge of q is injected midway between the plates of a capacitor that has a uniform electric field of E. What is the acceleration of this particle due to the electric field?

Eq/m

Which of the following best describes the motion of a negatively charged particle after it has been injected between the plates of a charged, parallel-plate capacitor?

It accelerates toward the positive plate.

In Figure 1, the maximum electrical potential energy occurs at:

A and C only

A plasma wave moving through a plasma has a frequency of 10⁹ Hz and a speed of 3.0 × 10⁷ m/s. What is the wavelength of this wave?

3.0 cm

Consecutive resonances occur at wavelengths of 8 m and 4.8 m in an organ pipe closed at one end. What is the length of the organ pipe? (Note: Resonances occur at L = nλ/ 4, where L is the pipe length, λ is the wavelength, and n = 1, 3, 5,…)

6.0 m

Which action requires a larger absolute value of work: lifting the weight from A to B with constant speed, or lowering the weight from B to A with the same constant speed?

Equal absolute value of work in both actions

A 1.00-kg object is initially at rest. The student applies a force of 19.6 N through a distance of 0.50 m to propel the object straight upward. It has an initial speed v and reaches a peak height h above the launch point.

How much work is done in launching the object?

9.8 J

A 1.00-kg object is initially at rest. The student applies a force of 19.6 N through a distance of 0.50 m to propel the object straight upward. It has an initial speed v and reaches a peak height h above the launch point.

What is the magnitude of the detected sound frequency shift from 170 Hz during the projectile flight described in the passage

It falls to zero, then increases.

As the light passes from the air into the glass, it makes an angle θ_a in air and an angle θ_l in the lens material, relative to the normal at the surface. What equation relates the angles θ_l and θ_a?

nₐ sin θₐ = nᵢ sin θᵢ

Changing which of the following will change the focal length of the convex mirror in Figure 2?

Radius of curvature of the mirror

Visible light travels more slowly through an optically dense medium than through a vacuum. A possible explanation for this could be that the light:

is absorbed and re-emitted by the atomic structure of the optically dense medium.

When switch S is closed to the left, charge begins to accumulate on the capacitor. Charge cannot accumulate indefinitely because:

successive charges brought to the plates are repelled by charges accumulated earlier.

To keep the current constant during the discharge cycle:

the resistance R must be continually decreased.

Which circuit elements store energy?

I. Capacitors

II. Resistors

III. Batteries

I and III only

The intensity level of Sound B is 20 dB greater than the intensity level of Sound A. How many times greater is the intensity level of Sound B than the intensity level of Sound A?

100

In order to determine the relative speed of approach of a sound source by Doppler measurements, three of the following items of data are necessary. Which one is NOT required?

The distance between source and observer

If light bends less (lower index): The image would:

move closer to original position

If something has no charge, what happens in a magnetic field?

it goes straight

Which of the following describes the direction of motion of alpha, beta, and gamma rays in the presence of an external magnetic field?

Gamma rays travel straight; alpha and beta rays are bent in opposite directions.

Three balls with the same volume of 1.0 x 10^–6 m³ are in an open tank of water that has a density (ρ) of 1.0 x 10³ kg/m³.

Assume that the density of Ball 1 is 8.0 × 10² kg/m³. Ignoring the atmospheric pressure, what fraction of Ball 1 is above the surface of the water?

1/5