General Science - Physics MCQs

Notes:
Kelvin is the base unit of temperature (SI unit), having the unit symbol K. The Kelvin temperature scale has an absolute zero (0°K) below which temperatures do not exist. It is the lowest possible temperature. At this temperature there is no motion and no heat. It is equivalent to 0°K, or -273.15° C, or at -460° F.

Notes:
The first statement is incorrect because light takes 1.2 – 1.3 seconds to reach from moon to earth. Second statement is correct. The exact time taken is 8 min 19 seconds (Speed of light=300,000 kilometres per second mean distance of sun from Earth=14,96,00000 Kms . The time comes to be about 498.66 second.) Statement 3 is also incorrect. The first part of the statement is correct which says that It takes 4.22 years for the light to reach from the nearest star, however nearest star is Alpha proxima and not Alpha Centauri is not nearest. Nearest is Proxima Centauri and to reach from Alpha centauri it takes 4.40 years. Next is Barnard`s Star, which is 5.94 light years away from Earth.

Notes:
Svedberg unit (S/ Sv) is a unit for sedimentation coefficients. It offers a measure of size of the particle based on sedimentation rate under acceleration. It calculates how fast the particle settles to the bottom of the solution. Svedberg unit is a measure of time (exactly 10−13 seconds).

Notes:
When a glass rod is rubbed with silk, a positive charge develops on the glass rod and a negative charge is developed on silk. The glass rod transfers its electrons to the silk when it is rubbed with silk. Thus, glass rod has less number of electrons than the number of protons in the nucleus. Thus, on the whole, the glass rod gets positively charged. When an ebonite rod is rubbed with fur, a negative charge develops on ebonite rod and a positive charge develops on fur. Ebonite rod gains electrons from the fur when it is rubbed with fur. Thus ebonite has more negative charges as compared to positive charges in the nucleus. Thus, on the whole, ebonite rod gets negatively charged.

Notes:
Chief characteristics of an image formed in plane mirror are:

1. Image is erect and of equal size.
2. Image is virtual, it means the image cannot be taken on screen.
3. The distance of image from the mirror is same as the distance between object and mirror.
4. Image is laterally inverted. It means right hand side of the object appears as left hand side of the image and vice versa.

Notes:
Number of images = (360÷angle) – 1

• If the mirrors are placed at parallel to each other , the images will be infinite in numbers
• If the mirrors are placed at an angle of 90° with each other , 3 images will be produced.

The more we decrease the angle between the two mirrors from 90°, the more will be number of images.

• At 60° the number of images is 5′
• At 30°, the number of images will be 11.

This concept is the principle of working of the Kaleidoscopes that operate on multiple reflection, several mirrors are attached together. The three mirrors if set at 45° from each other, creates eight duplicate images of the objects, six at 60°, and four at 90°.

Notes:
Real images can be produced by concave mirrors and converging lenses. But a converging lens and concave mirror are also capable of producing virtual images if the object is within the focal length. Flat mirrors can never produce real image because, rays never really converge.

Notes:
Approximately 1/8 (12.5 %) of the ice is visible above water and 7/8 (87.5 %) of the ice is submerged below the surface. This is because ice and snow are less dense than water. Here we must note that if the iceberg is made up of only compact ice, its visible part may be even 1/10th part because the compact part is relatively denser. But the top of the iceberg is usually made up of snow which is not that much compact and that is why the correct answer of this question is 1/8th.

Notes:
Unstructured Supplementary Service Data is a type of communications protocol which is used by GSM cellular telephones to set up communication with the mobile network operator’s computers. It maintains a continuous session which enables the users receive immediate response. Short message service uses standardized communication protocols which enable user to exchange short text messages through cell phones. It is of a single instance type and can’t involve a continuous session. While per message length (7 bit character) in USSD is 182 alphanumeric characters , it is 160 alphanumeric characters for SMS.

Notes:
Uniform circular motion denotes the motion of an object in a circle at a constant speed. An object moves in a circle constantly changes its direction. Velocity and acceleration changes but the speed does not change.