(GPT) Unit 22 waves

What is an incident ray?

It’s the ray of light that travels toward a surface or boundary.

What is a reflected ray?

The ray that bounces off a surface after hitting it.

What is the normal line in a ray diagram?

An imaginary line drawn at 90° to the surface where light hits.

How are angles of incidence and reflection measured?

Both are measured between the ray and the normal.

What happens if a light ray hits the surface directly along the normal?

It reflects straight back on itself with 0° angle.

Why do mirrors produce clear images?

Because they have smooth surfaces that reflect light evenly (specular reflection).

Why do rough surfaces not produce clear images?

Light reflects unevenly in all directions—this is diffuse reflection.

What's an example of diffuse reflection?

White paper reflecting light in many directions.

Why does refraction happen?

Because light changes speed when it enters a medium with a different optical density.

What happens when light enters a denser medium?

It slows down and bends toward the normal.

What happens when light exits into a less dense medium?

It speeds up and bends away from the normal.

Why does a pencil look bent in water?

Refraction causes light to bend at the water surface, distorting the image.

What is total internal reflection (TIR)?

When light is completely reflected inside a medium instead of refracting out.

What conditions are needed for TIR to happen?

Light must go from a denser to a less dense medium and hit at an angle greater than the critical angle.

What are real-life uses of TIR?

Optical fibres (internet cables), endoscopes (medical imaging), and some decorations.

What is dispersion?

The splitting of white light into a spectrum of colours by a prism.

Why do colours spread out in a prism?

Each wavelength (colour) bends at a slightly different angle during refraction.

Which colour refracts the most?

Violet.

What are the primary colours of light?

Red, Green, and Blue.

What happens when you mix all three primary light colours?

You get white light.

Why does a red apple appear red in white light?

It reflects red and absorbs all other colours.

Why does the same red apple look black in green light?

No red light is present to reflect, so it appears black.

Why do black objects heat up more in sunlight?

They absorb all colours and reflect none, taking in more energy.

What are electromagnetic waves?

Transverse waves made of electric and magnetic fields that can travel through a vacuum.

What's the order of the EM spectrum from lowest to highest frequency?

Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma.

Do all EM waves travel at the same speed?

Yes, in a vacuum, they all travel at 300,000,000 m/s.

Which EM waves are ionising?

Ultraviolet, X-rays, and Gamma rays.

Why are gamma rays dangerous?

They can penetrate the body and damage or mutate DNA, possibly causing cancer.

What are radio waves used for?

Communication (radio, TV, satellites).

What are microwaves used for?

Heating food and satellite communications.

What are infrared waves used for?

Thermal cameras, remote controls, and heaters.

What is ultraviolet light used for?

Sterilisation, tanning, detecting fake banknotes.

How are X-rays used in medicine?

Imaging bones and internal structures.

What is a medical use of gamma rays?

Killing cancer cells and sterilising equipment.

What is a wave?

A wave is a vibration that transfers energy from one place to another without transferring matter.

What's the difference between transverse and longitudinal waves?

Transverse waves vibrate at 90° to the direction of travel (e.g., light). Longitudinal waves vibrate in the same direction as the wave travels (e.g., sound).

What parts make up a wave?

Rest position, displacement, peak, trough, amplitude, wavelength, time period, and frequency.

Do waves transfer matter?

No, they only transfer energy.

What type of wave is light?

A transverse wave.

Can light travel through a vacuum?

Yes, light doesn't need a medium.

How does light travel?

In straight lines.

What’s the speed of light in a vacuum?

Approximately 300,000,000 m/s.

What are luminous objects?

Objects that produce their own light, e.g., the Sun.

How can we see non-luminous objects?

They reflect light from luminous sources into our eyes.

What causes a shadow?

An object blocking light rays.

What’s the difference between opaque, translucent, and transparent objects?

Opaque blocks all light, translucent allows some light, transparent lets all light through.

How does the distance between an object and a light source affect the shadow?

Closer = bigger shadow, farther = smaller shadow.

What is the law of reflection?

Angle of incidence = angle of reflection.

What is specular reflection?

Reflection from a smooth surface where light bounces in one direction (like a mirror).

What is diffuse reflection?

Reflection from a rough surface where light scatters in many directions.

What are the properties of an image in a plane mirror?

Upright, same size, laterally inverted, virtual, same distance behind mirror.

What is refraction?

Bending of light when it enters a medium where its speed changes.

What happens when light enters a denser medium?

It slows down and bends toward the normal.

What happens when it goes into a less dense medium?

It speeds up and bends away from the normal.

What is the normal?

A line drawn at 90° to the surface at the point of contact.

What is total internal reflection (TIR)?

When light hits a boundary at a high angle and is completely reflected inside the denser medium.

What is the critical angle?

The smallest angle at which total internal reflection occurs.

Give two uses of TIR?

Optical fibres in internet cables and endoscopes in medicine.

What is white light?

A mix of different wavelengths (colours) of light.

How does a prism split white light?

Each wavelength bends differently, spreading out into a spectrum (dispersion).

Which colour refracts the most?

Violet.

What’s the order of spectrum colours?

Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV).

What are the primary colours of light?

Red, Green, Blue.

What are the secondary colours of light?

Magenta, Cyan, Yellow.

Why does a red apple look black in green light?

No red light to reflect.

What are electromagnetic waves?

Transverse waves made of vibrating electric and magnetic fields.

Can EM waves travel through a vacuum?

Yes.

What speed do all EM waves travel at in a vacuum?

300,000,000 m/s.

What's the order of the EM spectrum?

Radio, Microwave, Infrared, Visible, UV, X-rays, Gamma (Roman Men Invented Very Unusual X-ray Guns).