Waves and Their Properties

These question-and-answer flashcards cover fundamental definitions, properties, formulas, and practical applications related to mechanical and electromagnetic waves, including sound and light, ensuring comprehensive review for the exam.

What do waves transfer from one place to another?

Energy, without transferring matter.

What kind of medium do mechanical waves require?

They require a material medium—solids, liquids, or gases—to propagate.

Can electromagnetic waves travel through space? Why?

Yes. They do not need a material medium and can move through the vacuum of space.

How do electromagnetic and mechanical waves compare in speed through air?

Electromagnetic waves (light) travel much faster than mechanical waves (sound) in air.

Name the seven regions of the electromagnetic spectrum in order of increasing frequency.

Radio, Microwave, Infra-red, Visible light, Ultraviolet, X-rays, Gamma rays.

What is the speed of all electromagnetic waves in a vacuum?

3.0 × 10^8 m s⁻¹ (the speed of light).

Which EM waves have the longest wavelength and lowest frequency?

Radio waves.

Give two practical uses of microwaves.

Cooking/heating food and satellite or mobile-phone communications (including speed cameras).

In a transverse wave, how do particles oscillate relative to energy transfer?

Particles vibrate perpendicular to the direction of energy transfer.

In a longitudinal wave, how do particles oscillate relative to energy transfer?

Particles vibrate parallel to the direction of energy transfer.

Define wavelength (λ).

The distance between two successive crests or troughs of a wave; measured in metres.

Define amplitude (A).

Maximum displacement of a particle from its equilibrium position; indicates wave energy.

How does amplitude relate to wave energy?

Greater amplitude means greater energy carried by the wave.

Define frequency (f).

Number of complete waves passing a point each second; measured in hertz (Hz).

Define period (T).

Time taken for one complete wave to pass a point; measured in seconds.

What is the relationship between period and frequency?

T = 1 ⁄ f.

Define wave speed (v) using frequency and wavelength.

v = f × λ.

State the formula for distance travelled by a wave.

d = v × t.

When white light passes through a prism, what happens?

It splits (disperses) into seven colours of the visible spectrum.

On what physical quantity does the colour of visible light depend?

Its frequency or equivalently its wavelength.

Which colour of visible light has the longest wavelength?

Red light (longer λ, lower f).

Which colour of visible light has the shortest wavelength?

Blue (or violet) light (shorter λ, higher f).

On what does the brightness of light depend?

The wave’s amplitude (greater amplitude → brighter light).

What type of wave is sound?

A mechanical, longitudinal wave.

What is the approximate speed of sound in air at room temperature?

About 330–343 m s⁻¹.

How does sound speed in water compare to air?

Sound travels faster in water (≈1500 m s⁻¹) than in air.

List the three main aspects used to describe sound waves.

Pitch, Loudness, and Timber (quality).

What property of a sound wave determines its pitch?

Frequency—higher frequency equals higher pitch.

What property of a sound wave determines its loudness?

Amplitude—larger amplitude equals louder sound; measured in decibels (dB).

Why does the same note sound different on different instruments?

Because each instrument has a unique timber (quality) due to its harmonic content.

State the speed calculation for a wave with f = 5 Hz and λ = 3 m.

v = f × λ = 5 Hz × 3 m = 15 m s⁻¹.

If T = 0.25 s, what is the frequency?

f = 1 ⁄ T = 1 ⁄ 0.25 s = 4 Hz.

A wave travels at 340 m s⁻¹ for 2 s. How far does it go?

d = v × t = 340 m s⁻¹ × 2 s = 680 m.

If v = 300 m s⁻¹ and f = 10 Hz, find λ.

λ = v ⁄ f = 300 m s⁻¹ ÷ 10 Hz = 30 m.

How far will sound travel in air vs. water in 3 s (330 m s⁻¹ vs. 1500 m s⁻¹)?

Air: 330 m s⁻¹ × 3 s = 990 m; Water: 1500 m s⁻¹ × 3 s = 4500 m; difference = 3510 m.

What is a transducer?

A device that converts one form of energy into another.

Give two roles of transducers in mobile phones.

1) Microphone converts sound to electrical signals; 2) Speaker converts electrical signals back to sound.

How do mechanical wave speeds vary with medium density?

Mechanical waves (e.g., sound) generally travel faster in denser media (solids > liquids > gases).

Are all electromagnetic waves transverse?

Yes—all EM waves are transverse in nature.

Why do mechanical waves sometimes appear as transverse in drawings even if they are longitudinal?

For clarity; longitudinal sound waves are often sketched as transverse to show amplitude and wavelength.

Which travels faster in air: light or sound?

Light—approximately one million times faster (3×10^8 m s⁻¹ vs. ~340 m s⁻¹).

How does frequency affect wavelength for a fixed wave speed?

They are inversely related; higher frequency means shorter wavelength, λ = v ⁄ f.