CBSE 12TH PHYSICS - Online Test
Q1. Photoelectric effect is
Answer : Option B
Explaination / Solution:
When the light strikes on a metal surface, electrons on the surface of the metal get energy from the light and get emitted from the surface. It is found that there will be no photoemission from a metal surface below a certain frequency of light. The phenomenon of emission of photoelectron from a metal surface by light of suitable frequency is called photoelectric effect.
Q2. Electronic communication is not possible if
Answer : Option A
Explaination / Solution:
As the information or message is transmitted from the source to the receiver ,it is first converted into electrical signal which is then transmiited through the communication medium.Hence in electrical communication it is must to convert raw message or information into electrical signal.Else the electronic messages will not be transmitted.
Q3. Electric charge
Answer : Option C
Explaination / Solution:
Every matter is made up of atoms which contains protons, electrons and neutrons.
Protons are +ve charged particles and electrons are - ve charged particles.
Because of electric charge these particles experience a force in electrical fields.
Q4. In Geiger-Marsden experiment very small deflection of the beam was expected because
Answer : Option B
Explaination / Solution:
No Explaination.
Q5. Alternating current is so called because
Answer : Option D
Explaination / Solution:
Alternating Current is the current in which the polarity of source continuously changes on a fixed frequency. So the positive and the negative terminals ‘alternate’
Q6. Electric Potential V at a point in an electrical field is
Answer : Option D
Explaination / Solution:
Electric potential V is the work done in bringing unit positive charge from infinity to the point in an electric field, and the potential energy is the work done in bringing any finite charge from infinity to the point in an electric field. They are related as, .If q =1C,
Q7. A free neutron decays into
Answer : Option D
Explaination / Solution:
Free neutrons are unstable. A free neutron () decays into a proton (), an electron (), and an electron antineutrino (). This phenomenon is called beta decay.
Q8. Focal length of a mirror is given by
Answer : Option B
Explaination / Solution:
No Explaination.
Q9. direction of magnetic force on a positive charge moving in a magnetic field is given by
Answer : Option C
Explaination / Solution:
The force experienced by a charged particle in a magnetic field is given by .The right hand rule for vector product can be used to determine the direction of .
Q10. Potentiometer measures the potential difference more accurately than a voltmeter, because
Answer : Option D
Explaination / Solution:
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.
