BZT1 - Physics: Waves and Optics

Explanation:

Frequency measures the number of complete cycles of a wave occurring in one second. The standard unit of frequency is the hertz (Hz), named after the physicist Heinrich Hertz. One hertz corresponds to one cycle per second. Other units like decibels, newtons, or joules measure sound intensity, force, and energy, respectively, and are unrelated to frequency.

Correct Answer:

Hertz

Why Other Options Are Wrong:

Decibel

Decibels measure the intensity or loudness of sound on a logarithmic scale, not the number of wave cycles per second, so it is unrelated to frequency.

Newton

Newtons are units of force, not a measure of cycles or oscillations, making this option incorrect.

Joule

Joules quantify energy, not the rate of oscillations or cycles, so it cannot be used as a unit of frequency.

Explanation:

Gamma rays have extremely high energy and very short wavelengths, making them strongly ionizing. They can remove tightly bound electrons from atoms, breaking chemical bonds and damaging DNA, which can lead to mutations and cell death. While microwaves and visible light can cause some effects like heating or photochemical reactions, they lack the energy to ionize atoms. Radio waves have even lower energy and are generally not harmful at typical exposure levels.

Correct Answer:

Gamma rays, because they are a form of ionizing radiation with high energy.

Why Other Options Are Wrong:

Radio waves, because they have the longest wavelength.

Long wavelength corresponds to low energy, which is insufficient to ionize or damage cellular molecules significantly.

Microwaves, because they can heat tissues.

Although microwaves can cause heating, they are non-ionizing and generally do not directly damage DNA at normal exposure levels.

Visible light, because it can cause photochemical reactions.

Visible light is non-ionizing and lacks the energy required to break chemical bonds in DNA or cause direct ionization, limiting its ability to cause significant cellular damage compared to gamma rays.

Explanation:

A diverging lens spreads parallel incoming light rays outward, creating the appearance that the rays originate from a single point on the same side of the lens as the light source. This effect is achieved by a concave lens, which is thinner at the center than at the edges. The curved surfaces bend the light away from the central axis, producing a virtual, upright, and smaller image. Flat lenses or convex lenses do not create this diverging effect, and “More than one of these” is inaccurate because only the concave lens truly functions as a diverging lens.

Correct Answer:

Concave

Why Other Options Are Wrong:

More than one of these

This option is incorrect because only a concave lens consistently functions as a diverging lens. Neither a flat nor a convex lens creates the necessary outward-spreading refraction. Grouping multiple lens types together in this context suggests that more than one shape naturally causes divergence, which is not true in optical physics.

Flat

A flat lens does not significantly bend light rays, so it cannot cause light to diverge. With no curvature, the rays simply pass through with minimal refraction, leaving them parallel to their original path. Without a change in curvature, divergence cannot occur, making a flat lens unsuitable as a diverging lens.

Convex

A convex lens is thicker in the center and converges light rays to a focal point, the opposite of what is needed for divergence. Its geometry bends rays inward, focusing them to form real images. This focusing action disqualifies it as a diverging lens.

Explanation:

Each half-life reduces the amount of Carbon-14 by half. After one half-life, 50% remains; after two, 25% remains (50% × 0.5 = 25%). Thus, the presence of 25% of the original Carbon-14 indicates that two half-lives have passed, which is about 11,460 years.

Correct Answer:

half-lives (11460 years)

Why Other Options Are Wrong:

1 half-life (5730 years)

Only 50% of Carbon-14 would remain after one half-life, not 25%.

half-lives (17190 years)

Three half-lives would leave 12.5% of the original Carbon-14, which is less than the 25% measured.

half-lives (22920 years)

Four half-lives would reduce the Carbon-14 to about 6.25%, far lower than 25%.

Explanation:

The law of reflection states that the angle of incidence equals the angle of reflection, with both angles measured relative to the normal line. Since the incident light ray makes a 60-degree angle with the normal, the reflected ray must also form a 60-degree angle with the normal.

Correct Answer:

60 degrees

Why Other Options Are Wrong:

30 degrees

This is half the angle of incidence and does not satisfy the law of reflection.

15 degrees

There is no basis for such a small angle; it does not match the incident angle.

120 degrees

Angles are measured from the normal, not from the surface itself; 120 degrees is not applicable.

45 degrees

A 45-degree reflection would only occur if the incidence were 45 degrees, which is not the case here.

Explanation:

Focal length is the distance between a lens or mirror and its focal point, where parallel light rays converge (for a convex lens or concave mirror) or appear to diverge from (for a concave lens or convex mirror). This distance is a key parameter in optics that determines image formation, magnification, and the lens or mirror’s optical power. Wavelength, frequency, and amplitude describe properties of waves, not the geometry of lenses or mirrors.

Correct Answer:

Focal length

Why Other Options Are Wrong:

Wavelength

Wavelength measures the spatial length of one complete wave cycle and is unrelated to the physical distance between a lens or mirror and its focal point.

Frequency

Frequency refers to how many wave cycles occur per second, which is a temporal property of waves, not a spatial distance in optics.

Amplitude

Amplitude measures the maximum displacement of a wave from its equilibrium, indicating energy, but it does not describe any distance between a lens or mirror and its focal point.

Explanation:

Ionizing radiation carries enough energy per photon to remove tightly bound electrons from atoms, creating ions that can cause chemical changes and biological damage. Non-ionizing radiation lacks sufficient energy to remove electrons, so it cannot ionize atoms, though it may cause excitation or heating. The distinction is based entirely on photon energy, not on inherent harm, speed, or source. Examples of ionizing radiation include gamma rays and X-rays, while radio waves and microwaves are non-ionizing.

Correct Answer:

Ionizing radiation has higher energy and can remove tightly bound electrons, while non-ionizing radiation does not have enough energy to do so.

Why Other Options Are Wrong:

Ionizing radiation is always harmful, while non-ionizing radiation is always safe.

This is inaccurate because ionizing radiation can be controlled and used safely in medical imaging or treatments. Non-ionizing radiation can also have harmful effects, such as heating from microwaves, so safety depends on exposure, not type.

Ionizing radiation travels faster than non-ionizing radiation.

All electromagnetic radiation travels at the same speed in a vacuum (the speed of light). Speed is not a distinguishing factor between ionizing and non-ionizing radiation.

Ionizing radiation is only produced by artificial sources, while non-ionizing radiation is natural.

Ionizing radiation occurs naturally (e.g., cosmic rays, radon) as well as artificially (X-ray machines). Non-ionizing radiation is also both natural and artificial, so this distinction is incorrect.

Explanation:

Wavelength is defined as the distance between two consecutive points in phase on a wave, most commonly measured between two successive peaks (crests) or troughs. It represents the spatial period of the wave and is typically measured in meters. In optics and physics, wavelength is a fundamental property that determines the color of light in the visible spectrum and affects how waves interact with materials and obstacles.

Correct Answer:

The distance between two consecutive peaks of a wave

Why Other Options Are Wrong:

The number of cycles of a wave that occur in one second

This describes frequency, not wavelength. Frequency measures how many complete wave cycles pass a given point in one second and is expressed in hertz (Hz), which differs from the spatial measurement of wavelength.

The speed at which a wave travels through a medium

Wave speed refers to how fast the wave propagates through a medium and is usually measured in meters per second. While related to wavelength and frequency by the equation v = f × λ, it is a different property.

The energy carried by a wave

The energy of a wave depends on its amplitude and frequency but is not the same as its wavelength. Wavelength measures distance between peaks, not the amount of energy transmitted.

Explanation:

Refraction is the bending of a wave when it crosses the boundary between two media at an angle other than 90 degrees. This occurs due to a change in wave speed between the media, causing the direction of the wave to change. This definition applies to all types of waves, including light, sound, and water waves, and is central to understanding lenses, prisms, and other optical phenomena.

Correct Answer:

The bending of a wave as it passes at an angle from one medium to another

Why Other Options Are Wrong:

The change in frequency of a wave as it travels through different media

Frequency remains constant when a wave enters a new medium; only the speed and wavelength change, so this is incorrect.

The reflection of a wave off a surface

Reflection is a different phenomenon in which the wave bounces back into the original medium rather than bending into a new medium.

The absorption of a wave by a medium

Absorption involves the wave losing energy to the medium, not bending or changing direction, so this does not describe refraction.