Infrared radiation are detected by:

A beam of plane polarized light falls normally on a polarizer of cross sectional area 3 . Flux of energy of incident ray in 10^–3 W. The polarizer rotates with an angular frequency of 31.4 rad/sec. The energy of light passing through the polarizer per revolution will be

(a) 10^–4Joule

(b) 10^–3Joule

(d) 10^–1Joule

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A star producing light of wavelength 6000 Å moves away from the earth with a speed of 5 km/sec. Due to Doppler effect the shift in wavelength will be ( c = 3

(a) 0.1 Å

(b) 0.05 Å

(d) 1 Å

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The magnetic field at the origin due to a current element $\text{i}\text{d}\ \vec{\text{l}}$ placed at a position $\overrightarrow{\text{r}}$ is:

$\frac{\mu_0\text{i}}{4\pi}\frac{\text{d}\overrightarrow{\text{l}}\times\overrightarrow{\text{r}}}{\text{r}^3}$
$-\frac{\mu_0\text{i}}{4\pi}\frac{\overrightarrow{\text{r}}\times\text{d}\overrightarrow{\text{l}}}{\text{r}^3}$
$\frac{\mu_0\text{i}}{4\pi}\frac{\overrightarrow{\text{r}}\times\text{d}\overrightarrow{\text{l}}}{\text{r}^3}$
$-\frac{\mu_0\text{i}}{4\pi}\frac{\text{d}\overrightarrow{\text{l}}\times\overrightarrow{\text{r}}}{\text{r}^3}$

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A magnetic field can be produced by:

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Ratio of the wavelengths of first line of Lyman series and first line of Balmer series is

(a) 1: 3

(b) 27 : 5

(d) 4 : 9

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A hollow tube is carrying an electric current along its length distributed uniformly over its surface. The magnetic field:

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An NPN-transistor circuit is arranged as shown in figure. It is