BZT1 - Physics: Waves and Optics

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:

Waves are traveling disturbances that propagate energy through a medium (mechanical waves) or through space (electromagnetic waves) without the bulk movement of matter. They can involve oscillations of particles, such as in water or sound waves, or oscillations of electric and magnetic fields, such as in light. Waves transmit energy from one point to another while the medium itself does not experience net displacement over long distances.

Correct Answer:

travelling disturbances

Why Other Options Are Wrong:

electromagnetic light

Light is one type of wave (electromagnetic), but this option is too narrow. Waves include mechanical waves, water waves, sound waves, and more, so defining waves only as light is incorrect.

sunlight and ocean waves

This mixes specific examples rather than giving a general definition. Waves are a broader concept encompassing many types beyond sunlight and water waves.

when somebody throws a rock at you

This describes an event, not a physical phenomenon. A rock being thrown is not a wave, although it may generate waves in a medium upon impact.

oscillations

Oscillations describe a periodic motion, but waves specifically involve the propagation of disturbances through space or a medium, which is more than just oscillation. Oscillations alone do not necessarily constitute a wave.

Explanation:

A convex mirror curves outward, causing reflected light rays to diverge and producing a virtual image that is smaller than the actual object but covers a wider field of view. This allows drivers to see more of the road behind them, reducing blind spots and improving situational awareness. However, because the images are smaller, objects appear farther away than they really are, so drivers must be cautious when judging distances.

Correct Answer:

The convex mirror provides a smaller, wider view, improving situational awareness

Why Other Options Are Wrong:

The convex mirror shows a larger image, making it harder to judge distances

A convex mirror produces a smaller, not larger, image, so this statement is inaccurate.

The flat mirror shows a distorted image, leading to confusion

A flat (plane) mirror provides an undistorted image of the same size as the object, so this description is incorrect.

The flat mirror provides a wider view but at a greater distance

A flat mirror does not provide a wider field of view than a convex mirror and does not change the perceived distance beyond normal reflection.

Explanation:

According to the law of reflection, the angle of incidence equals the angle of reflection. This means that if a light ray strikes a surface at an incident angle of 50˚ relative to the normal, it will reflect off the surface at the same angle, 50˚. The equality of these angles is a fundamental principle of reflection for all types of waves.

Correct Answer:

50

Why Other Options Are Wrong:

54

This angle is incorrect because the law of reflection requires the reflected angle to exactly match the incident angle.

55

A reflected angle of 55˚ would violate the law of reflection, as it does not equal the incident angle of 50˚.

60

Similarly, 60˚ is not equal to the incident angle, making it inconsistent with the fundamental rule that the angle of reflection equals the angle of incidence.

Explanation:

When light moves from a less dense medium (like air) to a denser medium (like water or glass), its speed decreases due to the higher optical density. This reduction in speed causes the light to bend toward the normal line at the boundary between the two media, as described by Snell’s law. The bending ensures the wavefronts remain continuous across the interface. This behavior is a fundamental property of refraction and explains phenomena such as objects appearing bent in water.

Correct Answer:

Because light travels slower in denser media, causing it to change direction.

Why Other Options Are Wrong:

Because the speed of light increases in denser media.

The speed of light actually decreases in a denser medium due to higher optical density. Increased speed would cause light to bend away from the normal, which contradicts observed refraction behavior.

Because the angle of incidence is greater than the angle of refraction.

While this statement is often true in magnitude, it is a description of the result, not the underlying cause. The bending occurs due to a change in speed, not because of the angle itself.

Because light rays are absorbed by denser media.

Absorption relates to energy loss, not the change in direction of light. Refraction occurs regardless of whether the medium absorbs light; it is caused by a change in light speed, not energy absorption.

Explanation:

When light passes from one medium to another—such as from air to water—its speed changes because the optical density of the mediums differ. This change in speed causes the light to bend at the interface, a phenomenon known as refraction. Refraction is responsible for effects like a straw appearing bent in a glass of water.

Correct Answer:

Refraction

Why Other Options Are Wrong:

Reflection

Reflection is the bouncing back of light from a surface without a change in speed or medium.

Diffraction

Diffraction is the bending and spreading of light around obstacles or through narrow openings, not a speed change between media.

Dispersion

Dispersion occurs when white light separates into its component colors, as in a prism, due to different wavelengths refracting at slightly different angles, but it is not simply the speed change when entering another medium.

Explanation:

The bending of light as it moves from one medium to another of different optical density is known as refraction. When light travels from a less dense medium, such as air, into a denser medium, like water or glass, its speed decreases, causing the light ray to bend toward the normal line. This change in direction due to a change in speed is the essence of refraction and is described by Snell’s law.

Correct Answer:

Refraction

Why Other Options Are Wrong:

Reflection

Reflection occurs when light bounces back from a surface without entering a new medium. It does not involve the light changing speed or direction within another substance.

Diffraction

Diffraction is the spreading of light around edges or through openings, which is different from bending due to a change in medium.

Dispersion

Dispersion refers to the separation of light into its component colors due to different wavelengths refracting by different amounts, such as in a prism. While related to refraction, it specifically describes wavelength-dependent separation, not the general bending of light entering a denser medium.

Explanation:

James Clerk Maxwell’s greatest contribution was unifying electricity, magnetism, and light into a single comprehensive theory. His set of equations, known as Maxwell’s equations, mathematically described how electric and magnetic fields interact and propagate as electromagnetic waves. This work demonstrated that light itself is an electromagnetic wave, providing the foundation for modern physics and technologies such as wireless communication and optics.

Correct Answer:

He unified electricity, magnetism, and light into a single theory.

Why Other Options Are Wrong:

He developed the theory of relativity.

The theory of relativity was developed by Albert Einstein, not Maxwell. While Maxwell’s equations influenced Einstein’s work, relativity is a distinct framework describing the relationship between space, time, and gravity.

He formulated the laws of motion.

The laws of motion were formulated by Sir Isaac Newton, centuries before Maxwell’s research. Maxwell’s contributions focus on electromagnetic phenomena, not classical mechanics.

He discovered the electron.

The electron was discovered by J.J. Thomson in 1897, long after Maxwell’s time. Although Maxwell’s theory laid the groundwork for understanding electromagnetic fields where electrons play a role, he did not discover the particle itself.

Explanation:

The number of cycles a wave completes per second is defined as its frequency. Frequency is measured in hertz (Hz), where one hertz equals one cycle per second. Wavelength measures the spatial distance between successive wave peaks, amplitude measures wave height, and speed refers to the distance traveled by a wave per unit time. Therefore, the correct term describing cycles per second is frequency.

Correct Answer:

frequency

Why Other Options Are Wrong:

wavelength

Wavelength is the distance between two successive crests or troughs, not the number of cycles per second, so it does not describe frequency.

amplitude

Amplitude measures the maximum displacement of the wave from its equilibrium position, which is unrelated to the number of cycles per second.

speed

Wave speed indicates how fast the wave travels through a medium, not how many cycles occur per second, making it incorrect in this context.