- AAc only
- BDc only
- CEither ac or dc
- DNeither dc nor ac
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$=\text{R}$
$\le\text{R}$
$>\text{R}$
$\ge\text{R}$
In the adjacent diagram, CP represents a wavefront and AO & BP, the corresponding two rays. Find the condition on q for constructive interference at P between the ray BP and reflected ray OP

|
(a) cosq = 3l/2d |
(b) cosq = l/4d |
(c) secq – cosq = l/d |
(d) secq – cosq = 4l/d |
A lamp rated at 100 cd hangs over the middle of a round table with diameter 3 m at a height of 2 m. It is replaced by a lamp of 25 cd and the distance to the table is changed so that the illumination at the centre of the table remains as before. The illumination at edge of the table becomes X times the original. Then X is
|
(a) |
(b) |
(c) |
(d) |
A 100 V voltmeter of internal resistance 20 kQ in series with a high resistance R is connected to a 110 V line. The voltmeter reads 5 V, the value of R is
|
(a) 210 kΩ |
(b) 315 kΩ |
(c) 420 kΩ |
(d) 440 kΩ |