Test: Modern Physics - Software Development MCQ

Concept:

Latent heat: It is the amount of heat needed to change the state of a unit mass of any substance without changing its temperature.

i.e., we can say that heat needed to supply for changing its state will be directly proportional to the mass m of the substance.

∴Q ∝ m

i.e.,Q = mL

The SI unit of Latent heat is J/Kg and the CGS unit is Cal/g respectively.

Where,

m = mass of an object

L = Latent heat

Q = amount of heat needed to change the state of matter of mass m 

Explanation:

From the above explanation, we can see that Amount of heat needed to melt a unit mass of a substance is directly proportional to the amount of mass of an object since the Latent heat of a material is constant.

i.e., Q ∝ m ⇒ Q = mL

Thus the unit of latent heat can be expressed as 

The correct answer is Mercury.

Key Points

• Mercury is used in thermometers because it remains in liquid form throughout a wide range of temperatures i.e -37.89 degrees Fahrenheit to 674.06 degrees Fahrenheit.
• The mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam.
• Mercury has a greater coefficient of thermal expansion than alcohol. 
• A thermometer with alcohol is used to measure low temperature because its freezing point is low i.e -1170C.
• It is Impossible to measure high temperatures because it’s a low boiling point.
• The thermometer with mercury cannot be used to measure the very low temperature because its freezing point is high i.e -38.88 °C.
• Mercury is the only one in liquid state at room temperature.
• It's used in thermometers because it has a high coefficient of expansion.
• It also has a high boiling point which makes it very suitable to measure higher temperatures. 
• It has a shiny appearance and doesn't stick to the glass surface of the glass.

Concept:

• Heat Transfer: Heat is transferred from one place to another in a substance due to temperature differences. 
  
• Evaporation: In this process, the liquid form a substance tends to convert in the gaseous phase on the uppermost surface due to heat and pressure.
• Condensation: In this process, the gaseous phase of an object tends to convert into liquid form due to pressure and temperature.

Explanation:

The other end of a wooden spoon will not become cold when it is dipped in a cup of ice cream because wood is a bad conductor, not a good conductor.

Concept:

• Electromagnetic waves or EM waves (Lightwave): The waves that are formed as a result of vibrations between an electric field and a magnetic field and they are perpendicular to each other and to the direction of the wave is called an electromagnetic wave.
• The accelerating charged particle produces an electromagnetic (EM) wave.
• A charged particle oscillating about an equilibrium position is an accelerating charged particle.
• Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons.
• Hence they can move in a vacuum 

Properties of Lightwaves:

• Not have any charge or we can say that they are neutral.
• Propagate as a transverse wave with both wave and particle nature.
• They move with the velocity the same as that of light i.e 3 × 108 m/s.
• It contains energy and they also contain momentum.
• They can travel in a vacuum also and always travel in a straight line.

Explanation:

• All of the above-given statements are true.
• Light travels in a straight line until its path is obstructed.
• Light has dual nature, that is, it shows both waves as well as particle nature.
• Light is a transverse wave as the particles of lightwave vibrate in a direction perpendicular to the direction of propagation.

Concept:

• Supersonic speed: An object moving with a speed greater than the speed of sound is said to move with a supersonic speed.
  • Generally, a bullet fired from a gun and aircraft moves with supersonic speed. 
  • The speed of sound is about 768 miles per hour (1,236 kilometers per hour) at sea level.
• Supersonic speeds are described by their "Mach number".
• Mach number: The ratio of the speed of the object to the speed of sound in the air of the same temperature and density is called Mach number.
  • Supersonic includes speeds up to five times faster than the speed of sound, or Mach 5.

Explanation:

• When the speed of any object exceeds the speed of sound, it is said to be traveling at Supersonic speed. So option 2 is correct.

Extra Points:

• Subsonic has a speed of less than 0.8 Mach.
• Hypersonic may have a speed between 5-10 Mach.

Concept:

• Ultrasonic waves are the sound waves with frequencies higher than the upper audible limit of human hearing.
  • They have a short wavelength.
• Echo: If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
  • Echoes are heard due to the phenomenon of Reflection of sound waves.
• SONAR: It a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water
  • SONAR stands for ‘Sound Navigation and Ranging.’
  • SONAR is based on the principle of echo.
  • Sonar is often used as a measurement of acoustic location and echo characteristics of the target object in the water.
  • It sends ultrasonic waves towards the bottom area of the sea and after reflection, the sound comes to the ship. We measure the time taken by the sound wave and then we get the depth. 

Explanation:​

• From the above discussion, we can say that the SONAR uses the principle of reflection of sound waves(Echo) to detect and locate objects. So option 2 is correct.
• Reverberation: The persistence of sound in a closed enclosure, due to continuous reflections at the walls or the floor or the ceiling of the enclosure, even after the source has stopped producing sound is known as 'reverberation'.

Concept:

• Semiconductor: The material which is not a good conductor or a good insulator is called a semiconductor.
  • For example: Silicon, Germanium, etc
• Intrinsic semiconductor: The pure form of semiconductor is called an intrinsic semiconductor.
• Extrinsic semiconductor: The impurity atoms added are called dopants and semiconductors doped with the impurity atoms are called extrinsic or doped semiconductors.

  • P-type semiconductor: The semiconductor having holes as majority charge carriers and electrons as a minority charge carrier is called as P-type semiconductor.

  • N-type semiconductor: The semiconductor having electrons as majority charge carriers and holes as a minority charge carrier is called as N-type semiconductor.

Explanation:

• ​From the above discussion, we can say that electrons are the major charge carriers in n-type semiconductors.

Important Point

• Elements of Group 5 have five valence electrons, i.e. 1 extra from the Group 4 elements.
• 4 out of 5 electrons get bonded with the neighboring Silicon atoms and 1 electron per atom remains extra with the Group 5 elements.

The correct answer is A thin layer of silicon.

Key Points

• In computers, the chip is made up of a thin layer of silicon.
  • Computer chips are made of silicon, which is a semiconductor, and in order to make the most efficient use of it, chip manufacturers use sand that contains as much silicon as possible.
  • The mineral quartz is ideal for this purpose because its two main components are silicon and oxygen.
  • Silicon is used because it can be used as either an insulator (doesn't allow electricity to flow) or a semiconductor (allows a little flow of electricity).
  • This is important for making chips.
  • It is very, very cheap.
• Hence, option 2 is correct. 

Additional Information

• Silicon is used for electronic devices because it is an element with very special properties.
  • One of its most important properties is that it is a semiconductor.
  • This means that it conducts electricity under some conditions and acts as an insulator under others.
  • It is even the most common element in the Earth's crust. 
• Lady Ada Lovelace invented looping in computer programming​.
  • Lady Ada Lovelace wrote a complete plan describing the algorithm needed to calculate the Bernoulli numbers using two loops, demonstrating the bifurcation capabilities of the analytical machine, describing how to perform trigonometric operations that made use of variables.

Concept:

• Plane mirror: This mirror is straight without any inward or outward curve.
  • It forms a virtual image and upright image which is of size as same as the object.
  • The bathroom mirrors are an example.
• Concave mirror: The mirrors curved inside on the reflecting side are called concave mirrors.
  • These mirrors produce a real, inverted, and magnified image of the object.
  • These are used in reflecting telescopes, shaving mirrors, and ophthalmoscope.

• Convex mirror: It is an outward curved mirror that produces a diminished image.
  • Convex mirrors either diverge a parallel beam of light into all directions or gather light from all directions and produce a parallel beam out of it.

Explanation:

• Following are the reasons as to why a convex mirror is used as a rearview mirror in the vehicle

• The image formed by the convex mirror is virtual and erect in contrast to that of the real but inverted image of the concave mirror.
• It gathers light from all directions and aligns it as a parallel beam so that it provides a wider view to the viewer. That's why the convex mirror is used as a rear-view mirror in vehicles. So option 2 is correct.

Concept:

• Power is the ability to bend light and it is equal to the reciprocal of the focal length of the lens/mirror in meters.

Power (P) = 1/f
Where f is the focal length of the lens/mirror.

Explanation:
As explained above, Dioptre is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres.
And since the S.I unit of the focal length is the meter (m).
So the S.I unit of power = 1/(SI unit of focal length) = m^-1 = Dioptre (D).
1 m^-1 = 1 D