Which one of the following types of electromagnetic radiation causes certain substances to fluoresce? A. Cosmic rays
B. Ultraviolet rays
(C. X rays)
D. Infrared waves

A virtual image produced by a lens is always

A. located in front of the lens.
(B. located in the back of the lens.)
C. smaller than the object.
D. larger than the object.

Reflecting telescopes are popular because they're

A. more durable than a refracting telescope.
B. more powerful than a refracting telescope.
C. easier to build than a refracting telescope.
(D. smaller than a refracting telescope.)

The unit for measuring the rate at which light energy is radiated from a source is the

A. lux.
B. lumen.
(C. candela.)
D. Angstrom

A magnifying glass is an example of a _______ lens.

A. plano-concave
(B. plano-convex)
C. double-concave
D. converging

my answer is in ( ) and the answers are wrong please tell me the correct answer because i dont have a clue

1. Answer;

B. ultraviolet rays

Ultraviolet rays are the type of electromagnetic radiation that causes certain substances to fluoresce.

Explanation;

• UV light is an electromagnetic radiation present in sunlight, that is shorter in wavelength than visible light and longer than X-rays.
• Ultraviolet radiation is undetectable by the human eye, however, when it falls on certain substances, it may cause them to fluoresce that is emit electromagnetic radiation of lower energy, such as visible light.
• Fluorescence is a phenomenon that causes a mineral to glow within the visible spectrum when exposed to ultraviolet light.

2. Answer;

B. located in the back of the lens.

Explanation;

• Virtual images are those images that are locations from where lights appears to have converged. Additionally, virtual images can not be reproduced on a a screen, and occur on the opposite side of the object and are always upright.

• Virtual images are formed by the diverging or concave lenses or by placing the object inside the focal length of a converging lens. The image is located at the back of the lens.

3. Answer;

C. easier to build than a refracting telescope.

Explanation;

• Reflecting telescopes are those telescopes that uses mirrors to focus the light while refracting telescopes uses lenses to focus the light.
• Reflecting telescopes have many advantages over refracting telescopes. These includes, the fact that mirrors don't cause chromatic aberration and they are easier and cheaper to build large.
• Additionally, they are  easier to mount because the back of the mirror can be used to attach to the mount.

4. Answer

C. Lumen

The unit for measuring the rate at which light energy is radiated from a source is the  Lumen.

Explanation;

• Luminous flux is the time rate of the flow of light, or the visible energy produced from a certain light source.  It is the quantitative measure of brilliance of a light source. The unit of luminous flux is lumen (lm. 
• Luminous intensity on the other hand is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle. Luminous intensity is measured in Candela.
• We could say that one lumen is the luminous flux of the uniform point light source that has a luminous intensity of 1 candela.

5. Answer;

B. Plano-convex lens

A magnifying glass is an example of a plano-convex lens.  

Explanation;

• Convex lenses are types of lenses that are thicker at the center and thinner at the edges. Plano-convex lens is a type of convex lens.

• Plano-convex lenses are types of lenses that are positive focal length elements with one spherical surface and one flat surface.
• These types of lenses are designed for parallel light use or simple imaging. therefore they are ideal for all purpose focusing elements.
• Magnifying glass is a type of convex lenses and an example of plano-convex lens, that is used to produce magnified image of an object.