Physics Test - 3

The correct answer is option 2) i.e. elasticity

CONCEPT:

• Elastic behaviour of solids: Elasticity is the property of solid materials to return to their original shape and size after the forces deforming acting on them have been removed. 
  • Solids are made up of molecules that are held together by intermolecular forces.
  • When an external force acts on the solid, the molecules get displaced and cause deformation.
  • Once the force ceases to act, the intermolecular forces drive the molecules back to their original position. This is how materials attain their initial shape and size.
  • The forces acting on the materials generate stress. If continuous stress is applied beyond the elastic limit of a material, the material starts deforming.

EXPLANATION:

• Elasticity brings the objects back to their original shape and size i.e. resists permanent changes due to forces acting on them.
• Thus, the ability of a body to resist permanent changes to it under the influence of stress acting on it is termed elasticity.

Additional Information

• Rigidity: Rigidity is the ability of a solid to withstand deformation when it undergoes mechanical stress. Unlike elasticity, it does not undergo any change in shape and size.
• Plasticity: Plasticity is the ability of a solid material to undergo permanent deformation due to applied forces.
• Fluidity: Fluidity is the ability of a substance to flow.

CONCEPT:

• The device that stores electrical energy in an electric field is called a capacitor.
• The capacity of a capacitor to store electric charge is called capacitance.
• When combination, where two or more capacitors are connected in such a way that their ends are connected at the same two points and have an equal potential difference across them, is called the parallel combination of a capacitor.
• Equivalent capacitance (C_eq) for parallel combination:

C_eq = C₁ + C₂

• When two or more capacitors are connected end to end and have the same electric charge on each is called a series combination of the capacitor.
• Equivalent capacitance (C_eq) in series combination:

Ans: Option 3)

CONCEPT:

• Archimedes principle: Partially or completely submerged body in a fluid is acted upon by an upward force called buoyant force.
  • The magnitude of this force is equal to the weight of the fluid displaced by the body.

EXPLANATION:

• Lactometer: It is a device used to check the purity of milk.
  • It works on the principle of Archimede's principle.
  • A solid suspended in a fluid will experience a vertical force equal to the weight of the fluid displaced.
• Hydrometer: It also works on the Archimedes principle.
  • It is used to know the (specific) density of the fluid.
  • The lower the density of the fluid, the more the hydrometer will sink.

The correct answer is option 3)

CONCEPT:

• Saturation velocity: The maximum velocity of a charge carrier in a semiconductor is known as saturation velocity.
• Instantaneous velocity: The rate of change of position for a time interval (very small).
• ​Terminal velocity: It is the maximum velocity that an object attained when it falls through a fluid.
• Drift velocity: The average velocity that is gained by charged particles, (eg. electrons) in a material due to an electric field is called drift velocity.
  • When there is no electric field, Subatomic particles like electrons move in random directions all the time.
  • When electrons are subjected to an electric field, initially they do move randomly, but they slowly drift in one direction.
  • The electrons move in the direction of the electric field applied, with drift velocity.

EXPLANATION:

• The average velocity attained by charged particles, (eg. electrons) in a material due to an electric field is called drift velocity.
• So the correct answer is option 4.

​Additional Information

Drift velocity of the electrons is calculated by:

where v is the drift velocity, I is the current in the wire, n is the number density of free electrons in the wire, A is the cross-sectional area of the wire, and e is the charge on one electron.

The correct answer is Four times.

Key Points

Heating effect of current:

• When the ends of a conductor are connected to a battery, then the free electrons move and the electric current flows through the wire.
• These electrons collide continuously with the positive ions of the wire and thus the energy taken from the battery gets dissipated in the form of heat.
• The effect of electric current due to which heat is produced in a wire when current is passed through it is called the heating effect of current.
• The heat produced in the wire is,

CONCEPT:

• According to de Broglie matter has a dual nature of wave-particle.
• The wave associated with each moving particle is called matter wave.
• Characteristics of Matter waves:
  1. ​​The lighter the particle, the greater is the de Broglie wavelength.
  2. The higher the velocity of the particle, the smaller is its de Broglie wavelength.
  3. The de Broglie wavelength of a particle is independent of the charge or nature of the particle.
  4. The matter waves are not electromagnetic in nature. Only charged particles produce electromagnetic waves.​
• ​​de Broglie wavelength associated with the particle

Where, h = Planck's constant and P = Linear momentum of a particle

Photon

• ​​Photon: Photon is an elementary particle that has a zero rest mass and moves with the speed of light in a vacuum.
  • A photon is the “quantum of electromagnetic radiation”.
  • It is the smallest and the fundamental particle of electromagnetic radiation.

CALCULATION:

Concept:

The magnetic field due to a straight conductor is circular around the wire and follows the right-hand rule: if the thumb points in the direction of the current, the fingers curl in the direction of the magnetic field.

The induced current in the loop is governed by Faraday's Law and Lenz's Law

If the induced current in the loop is clockwise, it means the loop's magnetic field opposes the decreasing flux into the plane. This indicates that the magnetic field due to the wire is initially into the plane and decreasing.

Explanation:

To produce a clockwise induced current in the loop:

• The magnetic field created by the wire must initially be **into the plane**.
• The magnetic flux into the plane is **decreasing**, so the loop opposes this decrease by creating a magnetic field in the same direction (into the plane).
• For the magnetic field into the plane to decrease, the current in the wire must be **time-dependent and upward** (use the right-hand rule).

The current in the wire is time dependent and upwards.

CONCEPT:

• Projectile motion: A kind of motion that is experienced by an object when it is projected near the Earth's surface and it moves along a curved path under the action of gravitational force.

CONCEPT:

• Dispersion of light: The phenomenon in which a white light ray when falls on a prism get separated into its component colors is called dispersion of light.
• Primary rainbow: Primary rainbow is the result of One Total internal reflection and two refractions from the suspended raindrop.
  • Violet color forms on the inner edge and red color on the outer edge. Angles subtended with the direction of sun are 42˚ (red) and 40˚ (violet) above the horizon.
  • The primary rainbow is a result of a three-step process, that is, refraction, reflection, and refraction.

• Secondary Rainbow: Secondary rainbow is the result of two total internal Reflections (TIRs) and two refractions from the suspended raindrop.
  • In this rainbow red color appears on the inner edge while violet color appears on the outer edge which is reverse of that of primary rainbow.
  • This is because of additional reflection which causes 180˚ phase shift.

EXPLANATION:

• The primary rainbow occurs due to two refractions and one internal reflection in the raindrop. So option 2 is correct.