Question

Select correct alternative
Statement -1 : Two thin lenses of power + 4D and - 2D are in contact. The focal length of the combination is 50 cm.
Statement -2 : The maximum kinetic energy of a photoelectron is 3 eV then stopping potential must be less than 3V.
Statement -3 :When a charge particle is released in uniform magnetic field it may perform circular motion due to magnetic force.

• A. FFF
• B. TFT
• C. TFF
• D. TTT

Answer 1

Answer: (C)

Statement 1: If $P_1$ and $P_2$ are the power of lenses of focal length $F_1$ and $F_2$ respectively , then focal length of the combination is $1/F=P_1+P_2$.
Statement 2: Stopping potential =( maximum kinetic energy)/ e.
Statement 3: $F=q\ast (v\times B)$ , Where F is force, q is charge of particle , v is velocity of particle and B is magnetic field . If v =0, then F=0 , so no circular motion takes place