Answer : Option BExplaination / 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. There will be no photoemission from a metal surface below a certain frequency of light. For photoemission minimum frequency of incident light is required. This minimum energy of an electron is called work function.
Answer : Option BExplaination / Solution:
When information are sent from one point to the other it has to be converted into electrical signal using transducer.The receiver receives it in its original from using receiver.Such from of communication is called electronic communication.
Q3.Which of the following methods can be used to charge a metal sphere positively without touching it . Select the best
Answer : Option CExplaination / Solution: This can be possible by induction, if a negative charge rod is placed near the sphere (at a distance not in touch) than it attracts positive charge inside the sphere towards its side and the negative charges collected on other side and when the surface of sphere connected to earth than the negative charge goes to earth and the sphere remain positively charged.
Answer : Option BExplaination / Solution:
The standard voltage and frequency of alternating current supply in India is set to 220 V and 50Hz respectively by the government of India because
when power has to be transmitted from a power plant, the biggest challenge is to cut the transmission losses. For this purpose, the current value should be small and potential difference(Voltage) should be more. Also losses are minimal at 50 Hz/60 Hz frequency.
Q6.Electric potential energy of two point charges q and q0 is
Answer : Option BExplaination / Solution: Potential energy of a system of charges is the work done in assembling the charges. Force between two charges q and q0 placed at a distance r apart is F=q0q4πε0r2Potential energy of the charges is given by℧=∫∞r−F∙dr=∫∞r−q0q4πε0r2dr=qq04πε0r
Q7.What is the unit of mass when measured on the atomic scale?
Answer : Option DExplaination / Solution:
The unified atomic mass unit (u) is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest.
Q9.Which of the following is most general charachteristic of Magnetic field
Answer : Option AExplaination / Solution: A moving charge experiences a force in a magnetic field called magnetic Lorentz force given byF⃗ =q(v⃗ ×B⃗ ).This force acts only if the particle (i) has charge q(ii) has a non zero velocity v and (iii) does not move parallel or anti parallel to the magnetic field B. A current carrying conductor placed in a magnetic field experiences a force given byF⃗ =Il⃗ ×B⃗