Physics Spring 2025 Semester Final Exam

What is resonance in the context of a sound wave?

• The increase in amplitude when a system vibrates at its natural frequency

• The decrease in sound intensity over time

• The bending of a wave as it passes through a new medium

• The change in wave frequency due to the Doppler effect

Answer explanation

Resonance occurs when a system vibrates at its natural frequency, leading to an increase in amplitude. This phenomenon enhances sound intensity, distinguishing it from other effects like sound intensity decrease or wave bending.

If you buy sunglasses in a store, how can you be sure that they are polarized?

• When one pair of sunglasses is placed in front of another and rotated in the plane of the body, the light passing through the sunglasses will be blocked at two positions due to refraction of light.

• When one pair of sunglasses is placed in front of another and rotated in the plane of the body, the light passing through the sunglasses will be blocked at two positions due to reflection of light.

• When one pair of sunglasses is placed in front of another and rotated in the plane of the body, the light passing through the sunglasses will be blocked at two positions due to the polarization of light.

• When one pair of sunglasses is placed in front of another and rotated in the plane of the body, the light passing through the sunglasses will be blocked at two positions due to the bending of light waves.

Answer explanation

The correct choice explains that when sunglasses are rotated in front of each other, light is blocked at two positions due to the polarization of light, confirming that the sunglasses are polarized.

If the speed of sound in air is 343 m/s and the wavelength of a sound wave is 1.5 meters, what is the frequency of the wave?

• 0.0044 Hz

• 229 Hz

• 514 Hz

• 513 Hz

Answer explanation

To find the frequency, use the formula: frequency = speed of sound / wavelength. Here, frequency = 343 m/s / 1.5 m = 229 Hz. Thus, the correct answer is 229 Hz.

If the temperature in the lab increases, what will happen to the measured speed of sound?

• It will decrease

• It will remain constant

• It will increase

• It will first increase, then decrease

Answer explanation

As temperature increases, the speed of sound in air also increases due to the greater energy of air molecules, which allows them to transmit sound waves more quickly. Therefore, the correct answer is that it will increase.

Which of the following real-life scenarios best illustrates the Doppler Effect?

• A. A flashlight beam spreading out in the dark

• B. A car horn sounds higher in pitch as it approaches and lower as it moves away

• C. An echo bouncing off a wall

• D. A tuning fork vibrating in the air

Answer explanation

Choice B illustrates the Doppler Effect, where the frequency of sound changes as the source moves towards or away from an observer, causing the car horn to sound higher in pitch when approaching and lower when receding.

What property of radio waves makes them useful for astronomical observations?

• They have long wavelengths and can pass through interstellar dust

• They are the only waves that can be detected in space

• They travel more slowly than other electromagnetic waves

• They have high energy and penetrate deep space

Answer explanation

Radio waves have long wavelengths, allowing them to penetrate interstellar dust that blocks visible light. This property makes them invaluable for astronomical observations, enabling the study of celestial objects obscured by dust.

Which of the following explains why X-rays can pass through the human body but are absorbed by bones?

• A. X-rays have very low energy and bounce off soft tissue

• B. X-rays are slower than visible light, allowing them to pass through

• C. X-rays are reflected by skin and absorbed by bone

• D. X-rays have high energy and are absorbed more by dense materials like bone

Answer explanation

X-rays have high energy, allowing them to penetrate soft tissues easily. However, they are absorbed more by dense materials like bone, which is why bones appear white on X-ray images.

Why do different elements produce unique emission spectra?

• Because they have different numbers of protons

• Because their electrons occupy different energy levels

• Because their nuclei emit different types of radiation

• Because their atoms vibrate at different frequencies

Answer explanation

Different elements have unique emission spectra because their electrons occupy different energy levels. When electrons transition between these levels, they emit specific wavelengths of light, resulting in distinct spectra for each element.

Which of the following best describes how an emission spectrum is created?

• A. Electrons absorb energy and move to higher energy levels, then emit photons as they return to lower levels

• B. Atoms reflect light at specific wavelengths, producing bright spectral lines

• C. A solid object emits all wavelengths of light, creating a continuous spectrum

• D. An object absorbs certain wavelengths, leaving dark gaps in the spectrum

Answer explanation

Choice A is correct because an emission spectrum is created when electrons absorb energy, jump to higher energy levels, and then emit photons as they return to lower levels, producing specific wavelengths of light.

Which of the following best describes the relationship between photon energy and wavelength in the electromagnetic spectrum?

• A. Longer wavelengths correspond to higher energy photons

• B. Shorter wavelengths correspond to higher energy photons

• C. Wavelength does not affect photon energy

• D. Photon energy depends only on temperature, not wavelength

Answer explanation

Photon energy is inversely related to wavelength. Shorter wavelengths, like those of gamma rays, have higher energy, while longer wavelengths, like radio waves, have lower energy. Thus, B is correct.