The magnifying power of a compound microscope is high if
 

1.  both the objective and the eyepiece has short focal lengths
2.  both the objective and the eyepiece have long focal lengths
3.  the objective has a short focal length and the eyepiece has a long focal length
4.  the objective has a long focal length and the eyepiece has a short focal length

Subtopic:  Simple & Compound Microscope |
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The following table 
 
is a truth table for
1. NAND gate
2. NOR gate
3. XOR gate
4. AND gate
Subtopic:  Logic gates |
 67%
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The half-life of a radioactive substance is 10 days. This means that

1.  The substance completely disintegrates in 20 days
2.  The substance completely disintegrates in 40 days
3.  1/8 part of the mass of the substance will be left intact at the end of 40 days
4.  7/8 part of the mass of the substance disintegrates in 30 days

From NCERT
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A source and an observer are moving towards each other with a speed equal to v/2, where v is the speed of sound. The source is emitting sound of frequency n. The frequency heard by one observer will be
1. zero
2. n
3. \(\frac{n}{3}\)
4. 3n
 54%
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Velocity of sound waves in air is 330 m/s. For a particular sound in air, a path difference of 40 cm is equivalent to phase difference of 1.6π. The frequency of the wave is
 

1.  165 Hz
2.  150 Hz
3.  660 Hz
4.  330 Hz

Subtopic:  Speed of Sound |
 59%
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