give brainliest pls thanksss
I’m not good at this but I’m guessing it’ll be the first one!
Answer:
See Explanation
Explanation:
1) Let us recall that;
Mass number = number of protons + number of neutrons
Where;
Number of protons = ?
Number of neutrons =20
Mass number =39
Number of protons = mass number - number of neutrons
Mass of protons =39 - 20= 19 protons
2) Atomic number = 13
Number of neutrons =14
Then the mass number =13 +14 =27
The symbol of the element is 27X13
The number of protons= the number of electrons =13
The atomic number is the same as the proton number =13
Real and virtual images.<span> In a dark room one can form an image of a candle flame on a white screen by letting the rays from the candle pass through a small opening. See Fig. 1. This idea is used in the pinhole camera. The pinhole camera is simply a light-proof box with a tiny pinhole in the front and photographic film stretched across the rear wall. See Fig. 2. One uncovers the pinhole for a minute or so, then covers it back up, to take a picture. If it is held steady, it can take a good picture. If one replaces the pinhole with a lens, the intensity of the incident light is increased and a sharp image can be recorded in a fraction of a second. The image formed by a pinhole or a lens is formed by incident rays of light on a surface and stands in contrast to another kind of image — the kind of image formed by a mirror. The image formed by a mirror is not real, it is an illusion formed by the way the light reflects off the mirror. The image seen in a mirror looks three dimensional and real but we know there is nothing where the image appears to be. An image such as that formed by a pinhole or lens is called a </span>real image<span>. An image such as that formed by a mirror is called a </span>virtual<span> image</span>
