Light, colours and beyond Flashcards

Flashcards based on Junior Secondary Science Mastering Concepts and Skills, focusing on light, reflection, refraction, lenses, and the electromagnetic spectrum.

What is the difference between luminous and non-luminous objects?

Luminous objects give out their own light (e.g., candle flame, the Sun), while non-luminous objects do not (e.g., whiteboard, street sign).

What are the three types of light beams?

Parallel, convergent, and divergent.

How do we see an object?

If the light it gives out enters our eyes or when it reflects light from other sources into our eyes.

Define incident ray, reflected ray, and normal in the context of reflection of light.

Incident ray: the light ray hitting the surface. Reflected ray: the light ray leaving the surface after reflection. Normal: An imaginary line perpendicular to the surface at the point where the incident ray hits the surface.

What are the laws of reflection?

The incident ray, the reflected ray, and the normal all lie in the same plane. The angle of reflection is always equal to the angle of incidence.

List four characteristics of an image formed by a plane mirror.

The same size as the object; laterally inverted; virtual; located behind the mirror with the image distance the same as the object distance.

What is refraction?

Refraction occurs when light travels through a boundary between air and a transparent medium at an angle.

How does light bend when entering a transparent medium from air?

Light bends towards the normal.

How does light bend when exiting a transparent medium into air?

Light bends away from the normal.

What is total internal reflection, and what are the conditions for it to occur?

Total internal reflection is when light is completely reflected at the boundary between two media. Conditions: Light travels from a medium of higher refractive index to a medium of lower refractive index; The angle of incidence is larger than the critical angle.

Give three examples of applications using prisms based on total internal reflection.

Binoculars, bike reflectors, cat’s eyes on highways.

Describe a convex lens.

A convex lens is thicker in the middle than at the edge.

What does a convex lens do to light rays?

A convex lens bends light rays towards the principal axis and can converge light.

Define optical center, principal axis, principal focus, and focal length of a convex lens.

Optical centre: the center of the lens. Principal axis: the line passing through the optical centre and perpendicular to the lens. Principal focus: the point to which light rays parallel to the principal axis converge after passing through the lens. Focal length: the distance of the principal focus from the optical center.

What are the possible characteristics of an image formed by a convex lens?

Real or virtual; Magnified, diminished, or the same size as the object; Erect or inverted.

List three construction rules for a convex lens.

A ray parallel to the principal axis is bent so that it passes through the principal focus on the other side of the lens. A ray passing through the principal focus emerges parallel to the principal axis. A ray passing through the optical centre travels straight on.

Describe a concave lens.

A concave lens is thinner in the middle than at the edge.

What does a concave lens do to light rays?

A concave lens bends light rays away from the principal axis and can diverge light.

What type of image is always formed by a concave lens?

Erect, diminished, and virtual.

List three construction rules for a concave lens.

A ray parallel to the principal axis is bent so that it appears to come from the principal focus. A ray directed towards the principal focus is bent parallel to the principal axis. A ray passing through the optical center travels straight on.

What is the electromagnetic spectrum?

The electromagnetic spectrum consists of visible light and other electromagnetic radiations or waves that cannot be seen by human eyes.

List the components of the electromagnetic spectrum.

Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, gamma rays.

Give examples of applications of radio waves.

Autotoll of vehicles, anti-shoplifting tags, wireless network using Wi-Fi and Bluetooth, short range communication using walkie-talkies, contactless payment using Octopus cards, mobile phone communication.

Give examples of applications of microwaves.

Heating up food, radars to locate aircraft and rainstorms, satellite telecommunications.

Give examples of applications of infrared radiation.

Heating (e.g., in halogen ovens), imaging (e.g., in some CCTV cameras), and signal transfer (e.g., in remote controls).

Give examples of applications of ultraviolet radiation.

Sterilization and checking banknotes.

Give examples of applications of X-rays.

Medical imaging (e.g., X-ray imaging, CT scans) and examining objects in luggage by customs officers.

Give examples of applications of gamma rays.

Cancer treatment, medical imaging, and food preservation.

Which electromagnetic radiations are more dangerous, and why?

Those of shorter wavelengths are more dangerous because they have higher energy.

What are the potential hazards associated with ultraviolet radiation?

Sunburn, skin cancer, cataracts.

What are the potential hazards associated with X-rays and gamma rays?

Cancer and DNA mutation.