Free Practice Questions for Physics in General-studies

The full form of LED is Light Emitting Diode.

Important Points:

• LEDs convert electrical energy into light. 
• LEDs are available in many colours such as red, green, yellow, blue, white. It is used in traffic signal lights and for lighting, etc. 
• A cluster of white LEDs grouped together forms a LED light source. 
• LED light sources consume less electricity and have a longer lifetime than light bulbs and fluorescent tubes. Hence these are gradually becoming the preferred lighting source.
• The compound semiconductor Gallium Arsenide- Phosphide is used for making LEDs of different colours.
• LEDs find extensive use in remote controls, burglar alarm systems, optical communication, etc.

Lead acid cells are not used in watches.

Important Points:

• Lead acid cell is a secondary cell. It consists of a grid of lead filled with lead dioxide (PbO2) as the anode and 38% sulfuric acid as the electrolyte.
• It is also known as accumulator cell. It is used in automobiles and inverters.
• The primary cell undergoes the reaction only once and dies after use. Examples are dry cell, mercury cell, silver oxide cell, zinc-air cell.
• Dry cells are used in transistors and clocks. They are also known as Leclanche cells.
• Mercury cells are used in low current devices such as hearing aids, watches, etc.
• Silver oxide cells are used in watches, calculators, photoelectric exposure devices, hearing aids, and electronic equipment.
• Zinc air cells are used as power sources for hearing aids, medical devices, and pagers.

Ringing of an alarm clock is part of quantum mechanics.

Important Points:

• The branch of science that takes into account the dual behavior of matter is called quantum mechanics.
• Alarm clock works on the concept of Quantum Mechanics.
• Quantum Physics involves the origin, propagation and properties of sound. 
• Examples of technologies powered by quantum mechanics include: MRI scanners for medical imaging, Lasers, Solar cells, Electron microscopes, Atomic clocks used for GPS, etc.
• Werner Heisenberg was awarded the Nobel Prize in Physics in 1932 for creation of the quantum mechanics. 

Electric field is a vector quantity.

Important Points:

• Electric field due to a charge Q at a point in space may be defined as the force that a unit positive charge would experience if placed at that point. SI unit of electric field is N/C or V/m. 
• Electric charge, electric flux and electric current are scalar quantities.
• A scalar quantity is a quantity with magnitude only.Example- Temperature, pressure, time etc.
• A vector quantity is a quantity that has both a magnitude and a direction.Example- Force, angular momentum, relative velocity etc.

Tonometer is a device that measures the pressure inside the eyes of a person.  

Important Points:

• It is used to test for glaucoma.

• Glaucoma is a serious eye disease that can lead the loss of vision. 

Options Explanation:

The minimum distance between two points in a wave having the same phase at a particular instant of time is called the wave length.

Important Points:

• If the constituents of the medium oscillate along the direction of wave propagation, we call the wave a longitudinal wave.
• If the constituents of the medium oscillate perpendicular to the direction of wave propagation, we call the wave a transverse wave.

A conservative force has the property that the work it does is independent of its path and depends only on its initial and final positions.

Important Points:

• Examples of conservative forces are gravitational force, elastic force, and electrostatic force. Not all forces are conservative. 
• Work done by a conservative force on an object is zero for a round trip of the object (the object returning back to its starting point). 
• The mechanical energy is conserved under conservative forces.

Biomass is not a biofuel.

Important Points:

• Some natural resources like coal, petroleum and natural gas were formed from the dead remains of living organisms millions of years ago. 
• These are all known as fossil fuels. 
• They are exhaustible resources. 
• They are the main source of conventional energy. 
• Coke, coal tar and coal gas are the products of coal. 
• Petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil, bitumen, and asphalt are obtained by refining petroleum.

Solids can be classified as crystalline or amorphous on the basis of the nature of order present in the arrangement of their constituent particles.

Important Points:

• Crystalline solids have a definite geometrical shape. 

Example - Sodium chloride and quartz.

• An amorphous solid made up of particles of irregular shape. 

Example - Glass, rubber, and plastics.

• Crystalline solids have a sharp melting point. 
• Amorphous solids are soft as compared to crystalline solids and can be molded and blown into various shapes.

Option Explanation:

• On the basis of their conductivities, solids can be classified into conductors, semiconductors and insulators.
• On the basis of their magnetic properties, solids can be classified into magnetic and non-magnetic solids.

A set of equations involving electric and magnetic fields, and their sources, the charge and current densities are known as Maxwell equations.

Important Points:

• The prediction emerge from Maxwell’s equations is the existence of electromagnetic waves, which are (coupled) time varying electric and magnetic fields that propagate in space.
• The speed of the waves, according to these equations, turned out to be very close to the speed of light ( 3 ×10⁸ m/s). 
• This led to the remarkable conclusion that light is an electromagnetic wave.

In the Millikan’s Oil Drop experiment, the oil drop is subjected to such forces whose nature does NOT fall under the category of magnetostatic.

Important Points:

• R. A. Millikan performed the oil-drop experiment for the precise measurement of the charge on an electron. 
• The charge on an oil-droplet was always an integral multiple of an elementary charge, 1.602 × 10 ^–19 C. 
• Millikan’s experiment established that electric charge is quantized.

Theory behind Millikan’s experiment

CHSL 14-10-2020 (Afternoon)

IMPORTANT FACTS

In the first paper Albert Einstein introduced the notion of light quanta (now called photons) and used it to explain the features of photoelectric effect. In the second paper, he developed a theory of Brownian motion, confirmed experimentally a few years later and provided a convincing evidence of the atomic picture of matter. The third paper gave birth to the special theory of relativity. In 1916, he published the general theory of relativity. In 1921, he was awarded the Nobel Prize in physics for his contribution to theoretical physics and the photoelectric effect.

IMPORTANT FACTS

Car moving on a straight road is an example of Rectilinear motion.

Important Points:

• When an object repeats a motion and repeats itself at regular time intervals, this type of motion is called harmonic motion.

• The back and forth motion of an object from its mean position is called oscillatory motion.

• The direction of motion of an object keeps changing continuously along a circular path, it is called circular motion.

• If every point on an object moves about a fixed axis, then the motion of the object is called rotational motion.

• If an object moves along a curved path, it is said to be in circular motion.

Zeeman effect is the name of the phenomena in physics and astronomy which involves the splitting of a spectra line into two or more components of slightly different frequency when the light source is placed in a magnetic field.

Important Points:

• Zeeman effect is named after the Dutch physicist Pieter Zeeman, who discovered it in 1896 and received a Nobel prize for this discovery.
• It is analogous to the Stark effect. 
• Stark effect is the splitting of spectral lines observed when the radiating atoms, ions, or molecules are subjected to a strong electric field
• It was discovered by a German physicist, Johannes Stark.

At a constant speed when an object follows a circular path , the motion of the object is called uniform circular motion. 

Important Points:

• The velocity of the object is changing continuously in direction, the object undergoes acceleration.
• The magnitude of its acceleration is a_c = v² /R. 
• The direction of acceleration is always towards the centre of the circle. 
• The direction of velocity is always perpendicular to the direction of acceleration. 
• Displacement can not be greater than the distance.

SSC CPO 12/12/2019 (Evening)

IMPORTANT FACTS

Velocity of Uniform Circular Motion :

• Velocity =  Circumference of circle / Time
• v = 2πr/ t

where,

• v - velocity of the object
• r - radius of the circular path
• t - time taken by the object

The velocity–time graph for a motion with constant velocity(having zero acceleration) is a straight line parallel to time-axis.

Important Points:

• The change in the position of the object is called displacement.
• Displacement is a vector quantity.
• The velocity-time (v-t) graph for a motion with uniformly increasing velocity is a straight line with a positive slope.
•  The v-t graph for a motion with a uniformly decreasing velocity is a straight line with a negative slope. 
• The acceleration of a moving body is equal to the slope of its v-t graph. 
• Greater the slope of a v-t graph, the greater the acceleration of the body. 

Twin paradox is associated with the theory of relativity.

Important Points:

• According to Einstein’s special theory of relativity, time does not pass in the same way for everybody and varies depending on the motion of the observer. 
• Following special theory of relativity, an apparent paradox was pointed out.
• This paradox became known as the twin paradox. 
• The twin paradox assumes that one of the two twins travels to space at 99.9% the speed of light and comes back to Earth.
• It suggests that when the traveling twin returns she is younger than her twin sister who stayed on Earth.

The Coriolis force is responsible for the rotation of the plane of oscillation of Foucault's pendulum.

Important Points:

• The apparent force due to the rotation of the Earth is called the Coriolis force. 
  
• The Coriolis force deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. It is also known as 'Farrell's Law'.
• The Foucault pendulum is a simple device named after the French physicist Léon Foucault,
• The Foucault pendulum was first used to demonstrate the rotation of the Earth.
• A long and heavy pendulum hanging from a high ceiling over a circular field
• The condition shows that the rotation of the Earth causes the plane of oscillation of the pendulum to rotate with respect to the surface beneath it.