CBSE 12TH PHYSICS - Online Test
Q1. If a positive charge moves opposite to the direction of the electric field
Answer : Option D
Explaination / Solution:
A positive charge experiences a force in the direction of the field. If it moves opposite to the direction of the field, negative work is done by the electric field on the charge. Potential energy of the charge increases since an external source is required to do work on the charge against the direction of the field, and the work done is stored in the charge as its potential energy.
Q2. According to Snell’s law
Answer : Option A
Explaination / Solution:
No Explaination.
Q3. Contains
Answer : Option A
Explaination / Solution:
Number of protons = Atomic number = 79
Number of neutrons = Atomic mass number - atomic number = 197-79 = 118.
Q4. correct expression for force on a current carrying conductor of length dl in a magnetic field is
Answer : Option B
Explaination / Solution:
force experienced by a conductor of length l carrying current I placed in magnetic field B is given by .Here =
Q5. The sensitivity of the potentiometer can be increased by:
Answer : Option A
Explaination / Solution:
A potentiometer is considered to be sensitive if the potential gradient is low. Such a potentiometer can measure very small changes in potential difference. Increasing the length of the potentiometer wire decreases the potential gradient. Its sensitivity increases. Increasing potential gradient decreases the sensitivity. increasing the emf of the primary cell and by decreasing the length, potential gradient increases.
Q6. According to Huygens construction relation between old and new wave fronts is
Answer : Option C
Explaination / Solution:
No Explaination.
Q7. Compass needle of known magnetic moment m in a uniform magnetic field field experiences a torque equal to
Answer : Option D
Explaination / Solution:
No Explaination.
Q8. Motion of hole is a convenient way of describing
Answer : Option A
Explaination / Solution:
The holes are just the abscence of a electron in a energy band. But its easier to describe the abscence of a electron as a single moving positive charge than it is to describe the motion of all the other electrons in the band.
In a band you have N electrons. Remove one of those electrons(by for instance p-doping) and you have N-1 electrons left. Now you can either choose to describe this with the behavior of those N-1 electrons. Or you can choose to describe it as if there is one single hole moving around in the band.
So mathematicly the holes behave just like a positivly charged electron.
Q9. Angular frequency ω and wave vector k are related by
Answer : Option D
Explaination / Solution:
No Explaination.
Q10. According to Farady's law for a coil having N turns, the total induced emf is given by
Answer : Option C
Explaination / Solution:
The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit.
induced emf for a coil having 1 turns will be
The flux of all the turns will be added up. So the induced emf for a coil having N turns will be
