11. Electrons were discovered by
- A. Dalton
- B. James Charwick
- C. J.J. Thompson
- D. Niels Bohr
Correct Option: Answer is C
Electron was discovered J.J Thompson in 1879
12. Which of the following is/are the limitations to the Rutherford’s atomic models?
I. It is applicable when energy is radiated as electrons are revolving
II. It is applicable when energy is radiated in a continuous mode
III. It is applicable to an atom with only one electron in the other shell
- A. I only
- B. II only
- C. I & II only
- D. I, II & III only
Correct Option: Answer is C
Rutherford assumed that (I) energy is radiated when electrons are revolving (II) energy is radiated in a continuous mode. These are limitations of Rutherford’s model
13. Which of the following equations is the correct definition of the reactance of an indicator L?
- A. Reactance = (Amplitude of voltage) (Amplitude of current)
- B. Reactance = (Amplitude of voltage) x (Amplitude of current)
- C. Reactance = (Amplitude of current)2 (Amplitude of voltage)
- D. Reactance = (Amplitude of current) (Amplitude of voltage)1/2
Correct Option: Answer is A
Reactance is the value of an indicator or a capacitor in ohms
14. Ripple in a power supply unit is caused by
- A. using an alternating current source
- B. forward voltage drop
- C. heavy load
- D. using a zener diode
Correct Option: Answer is D
The correct option is “Using a zener diode” as fluctuation of d.c signal results from the rectification of a.c to d.c.
15. When th temperature of a liquid is increased, its surface tension
- A. increases
- B. decreases
- C. remain constant
- D. increases then decreases
Correct Option: Answer is B
Surface tension or elasticity of a fluid decreases with increased in temperature
16. The distance between an object and its real image in a convex lens is 40cm. If the magnification of the image is 3, calculate the focal length of the lens
- A. 6.5 cm
- B. 7.5 cm
- C. 8.5 cm
- D. 4.5 cm
Correct Option: Answer is D
u + v = 40
\(\frac{v}{u}\) = 3
v = 3u
u + 3u = 40
4u = 40
u = 10cm
v = 3u = 30cm
f = \(\frac{uv}{u + v} = \frac{10(30)}{10 + 30} = \frac{300}{40}\)
= 7.5 cm
17. A ray of light passes through the centre of curvature of a concave mirror and strikes the mirror. At what angle is the ray reflected?
- A. 180
- B. 90
- C. 0
- D. 60
Correct Option: Answer is C
– a ray of light passing through the centre of a curvature is returned along the same path
– angle difference along the same path is zero
18. The pin-hole camera produces a less sharply defined image when the
- A. pin-hole is larger
- B. illumination is less
- C. screen is further from the pin-hole
- D. object is further from the pin-hole
Correct Option: Answer is A
– a less sharp or blurred image is due to increased brightness
– increase brightness is also due to large hole or many pin holes
19. A straight wire 15cm long, carrying a current of 6.0A is in a uniform field of 0.40T. What is the force on the wire when it is at right angle to the field
A. 0.46N
B. 0.35N
C. 0.36N
D. 0.24N
Correct Option: Answer is C
F = BIL = 0.4 x 6 x 15 /100
= 0.36N
20. The pitch of a screw jack is 0.45cm and the arm is 60cm long. If the efficiency of the Jack is 75/π %, calculate the mechanical advantage.
- A. 400
- B. 300
- C. 200
- D. 150
Correct Option: Answer is C
P = 0.45cm, L = 60cm, Eff = 75/π%
VR | (Screw | system) | = | 2πr P | = | 2πL P |
M.A | = | Eff% × VR 100 | = | 75 π | × | 1 100 | × | 2π × 60 0.45 | = | 75 × 800 300 | = | 200 |