16 cm
12 cm
To find the focal length of the lens, we use the lens formula:
\(\frac{1}{f} = \frac{1}{v} - \frac{1}{u}\)
where \(f\) is the focal length, \(v\) is the image distance, and \(u\) is the object distance. Given that the object distance \(u = -20\) cm (convention: object distance is negative) and the screen is 50 cm away from the object, the image distance \(v = 20 + 50 = 70\) cm.
Substitute these values into the lens formula:
\( \frac{1}{f} = \frac{1}{70} - \frac{1}{-20} \)
\( \frac{1}{f} = \frac{1}{70} + \frac{1}{20} \)
Convert to a common denominator:
\( \frac{1}{f} = \frac{20 + 70}{1400} = \frac{90}{1400} \)
Therefore, \( f = \frac{1400}{90} = \frac{140}{9} \approx 15.56 \text{ cm} \)
So, the focal length of the lens is 16 cm.
Match List-I with List-II for the index of refraction for yellow light of sodium (589 nm)
LIST-I (Materials) | LIST-II (Refractive Indices) | ||
---|---|---|---|
A. | Ice | I. | 1.309 |
B. | Rock salt (NaCl) | II. | 1.460 |
C. | CCl₄ | III. | 1.544 |
D. | Diamond | IV. | 2.417 |
Choose the correct answer from the options given below:
Match the LIST-I with LIST-II
LIST-I | LIST-II | ||
---|---|---|---|
A. | Compton Effect | IV. | Scattering |
B. | Colors in thin film | II. | Interference |
C. | Double Refraction | III. | Polarization |
D. | Bragg's Equation | I. | Diffraction |
Choose the correct answer from the options given below: