The counting rate observed from a radioactive source at t = 0 second was 1600 counts per second and at t = 8 seconds it was 100 counts per second. The counting rate observed, as counts per second at t = 6 seconds, will be
|
(a) 400 |
(b) 300 |
(c) 200 |
(d) 150 |
(c) 200
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Focal length of a plane mirror is
|
(a) Zero |
(b) Infinite |
(c) Very less |
(d) Indefinite |
The sun emits a light with maximum wavelength 510 mm while another star X emits a light with maximum wavelength of 350 nm. What is the ratio of surface temperature of sun and the star X
|
(a) 2.1 |
(b) 0.68 |
(c) 0.46 |
(d) 1.45 |
Eels are able to generate current with biological cells called electroplaques. The electroplaques in an eel are arranged in 100 rows, each row stretching horizontally along the body of the fish containing 5000 electroplaques. The arrangement is suggestively shown below. Each electroplaques has an emf of 0.15 V and internal resistance of 0.25 W
The water surrounding the eel completes a circuit between the head and its tail. If the water surrounding it has a resistance of 500 W, the current an eel can produce in water is about
|
(a) 1.5 A |
(b) 3.0 A |
(c) 15 A |
(d) 30 A |
The lines of forces due to earth's horizontal component of magnetic field are
| (a) Parallel straight lines | (b) Concentric circles |
| (c) Elliptical | (d) Parabolic |
A battery is charged at a potential of 15 V for 8 hours when the current flowing is 10 A. The battery on discharge supplies a current of 5 A for 15 hours. The mean terminal voltage during discharge is 14 V. The "Watt-hour" efficiency of the battery is
|
(a) 82.5% |
(b) 80 % |
(c) 90% |
(d) 87.5% |