Question Discussion & Solution

The correct answer is Light Pen.

Key Points 

• Light Pen -
  • It is an input device of the computer which serves to give commands to the computer.
  • It is also called an electronic pen.
  • It looks like an ordinary pen.
  • It is used as a mouse.

Additional Information 

• A wave of light emerges from the tip of this pen.
• With this point, the icon made on the screen is touched and clicked.
• This work is done in the same way that we click by moving the mouse pointer on the screen.
• The tip of the light pen acts in a way like the Enter / Ok button.​

CONCEPT:

Equilibrium of a rigid body:

• A rigid body is said to be in mechanical equilibrium if both its linear momentum and angular momentum are not changing with time, or equivalently, the body has neither linear acceleration nor angular acceleration.
• Condition for the mechanical equilibrium:
  1. The total force, i.e. the vector sum of the forces, on the rigid body is zero.
  2. The total torque, i.e. the vector sum of the torques on the rigid body is zero.

⇒ \(\rm\vec{F_1}+\vec{F_2}+...+\vec{F_n}=0\)

⇒ \(\rm \vec{τ_1}+\vec{τ_2}+...+\vec{τ_n}=0\)

• If the forces on a rigid body are acting in the 3 dimensions, then six independent conditions to be satisfied for the mechanical equilibrium of a rigid body.
• If all the forces acting on the body are coplanar, then we need only three conditions to be satisfied for mechanical equilibrium.
• A body may be in partial equilibrium, i.e., it may be in translational equilibrium and not in rotational equilibrium, or it may be in rotational equilibrium and not in translational equilibrium.

EXPLANATION:

• A rigid body is said to be in mechanical equilibrium if both its linear momentum and angular momentum are not changing with time, or equivalently, the body has neither linear acceleration nor angular acceleration.
• We know that the linear acceleration and the angular acceleration of a stationary body are zero.

A book is kept on a table:

• In this case, the book will be stationary so it is an example of the equilibrium of a body.

A ball is moving downward freely under gravity:

• We know that when a ball moves freely under gravity, then only the gravitational force will act on the ball due to which the ball accelerates downward.
• Therefore ball is moving downward freely under gravity is not an example of the equilibrium of a body.
• Hence, option 1 is correct.

Explanation:

• Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms.
• On the basis of origin, bacteria can be divided into two types - Archaebacteria & Eubacteria

Archaebacteria:

• These bacteria are special since they live in some of the harshest habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens).
• Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions.
• For example - Methanogens are present in the gut of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals.

Additional Information 

Eubacteria:

• There are thousands of different eubacteria or ‘true bacteria’.
• They are characterised by the presence of a rigid cell wall, and if motile, a flagellum.
• The Eubacteria can be both autotrophic & heterotrophic.

The correct answer is Archimedes' principle.

Concept:

Archimedes principle:

the principle of Archimedes states “When a body is immersed in a liquid, an upward thrust, equal to the weight of the liquid displaced, acts on it.”

Thus, when a solid is fully immersed in a liquid, it loses weight which is equal to the weight of the liquid it displaces.

i.e., \(Apperent\;weight = actual\;weight - buoyant\;force = mg - \rho gV\)

where m is mass of the object, ρ is the density of the fluid

Hence if there is no gravity, there is no Upward Thrust.

The upward force applied to the object is called the buoyant force.

Here,

ρ = density of liquid

g = acceleration due to gravity

V = volume of liquid displaced by the object

Explanation:

Archimedes’ principle, a physical law of buoyancy states that any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which is equal to the weight of the fluid displaced by the body.

Hence floating of the ship is based on Archimedes principle:

The correct answer is 1024 megabytes

The size of information in the computer is measured in Kilobytes (KB), Megabytes (MB), Gigabytes (GB), and Terabytes (TB).

• 1 Kilobyte (KB) = about 1 thousand bytes (or 1024 bytes to be precise)
• One Megabyte (MB) is about 1 million bytes (or about 1024 Kilobytes (KB)).
• One Gigabyte (GB) is about 1 billion bytes, or (1024 Megabytes MB).
• One Terabyte (TB) is about roughly 1 trillion bytes or 1024 gigabytes (GB).