CBSE 12TH PHYSICS - Online Test

Q1. If a charge moves in an electrical field
Answer : Option C
Explaination / Solution:

Ambiguous question. Energy may be gained or lost depending on the sign of the charge and the electric field. It can also remain unchanged if the charge moves perpendicular to the direction of the field.

Q2. Atomic mass unit (u) is defined as ________ of the mass of the carbon () atom.
Answer : Option B
Explaination / Solution:

For standardization, a specific atomic nucleus (carbon-12) had to be chosen because the average mass of a nucleon depends on the count of the nucleons in the atomic nucleus due to mass defect. This is also why the mass of a proton or neutron by itself is more than (and not equal to) 1 u.

Q3. According to Cartesian sign convention the heights measured
Answer : Option D
Explaination / Solution:
No Explaination.


Q4. which of the following best describes the difference between electric and magnetic fields
Answer : Option B
Explaination / Solution:

The electrostatic force experienced by a positive charge q placed in an electric field is . The force acts in the direction of the electric field.The magnetic force acting on a charge of magnitude q moving with a velocity 'v' is .This acts in a direction perpendicular to the plane containing the vectors.v and 
Q5. The instrument for the accurate measurement of the e.m.f of a cell is
Answer : Option D
Explaination / Solution:

Both potentiometer and voltmeter are devices to measure potential difference. E M F is the terminal p.d between the electrodes of a cell in open circuit, i.e., when no current is drawn from it. Potentiometer measures the potential difference using null deflection method, where no current is drawn from the cell; whereas voltmeter needs a small current to show deflection. So, accurate measurement of p.d is done using a potentiometer.



Q6. Emission and absorption is best described by,
Answer : Option A
Explaination / Solution:
No Explaination.


Q7. When iron filings are sprinkled on a sheet of glass placed over a short bar magnet then,
Answer : Option D
Explaination / Solution:

North pole act as positive end and South pole act as negative end. The iron fillings in the presence of magnetic field gets magnetized and form a tiny magnet which then gets attracted to the poles of bar magnet. North pole of bar magnet attracts south pole of tiny magnet and vice-versa. So all the iron fillings are arranged as the magnetic field lines of bar magnet.

Q8. In the case of semiconductors the valence and conduction bands have
Answer : Option C
Explaination / Solution:

The materials can be classified by the energy gap between their valence band and the conduction band. The valence band is the band consisting of the valence electron, and the conduction band remains empty. Conduction takes place when an electron jumps from valence band to conduction band and the gap between these two bands is forbidden energy gap. Wider the gap between the valence and conduction bands, higher the energy it requires for shifting an electron from valence band to the conduction band.

  • In the case of conductors, this energy gap is absent or in other words conduction band, and valence band overlaps each other. Thus, electron requires minimum energy to jump from valence band. The typical examples of conductors are Silver, Copper, and Aluminium.
  • In insulators, this gap is vast. Therefore, it requires a significant amount of energy to shift an electron from valence to conduction band. Thus, insulators are poor conductors of electricity. Mica and Ceramic are the well-known examples of insulation material.
  • Semiconductors, on the other hand, have an energy gap which is in between that of conductors and insulators. This gap is typically more or less 1 eV, and thus, one electron requires energy more than conductors but less than insulators for shifting valence band to conduction band.

Q9. Without the concept of displacement current it is not possible to correctly apply Ampere’s law on a path parallel to the plates of parallel plate capacitor C in
Answer : Option B
Explaination / Solution:
No Explaination.


Q10.

When current carrying coil  is moved towards the coil  connected in series with a galvanometer, the pointer in the galvanometer G


Answer : Option C
Explaination / Solution:

current induced due to flux changed when C2 is in motion .