Railway Board offers opulent and revered job posts to its aspirants. And it is not every year that we get the notification from Railway offering a good number of vacant seats to the multitude aspirants. But the current year 2018 brought a pleasant surprise with almost 1,27,278 seats to be filled by the valid candidates. Opportunity is here but you have to welcome it with a provident strategy.
निम्नलिखित विकिरणों में से, किसमें उच्चतम ऊर्जा है
(a) Visible / दृश्यता
(b) X-ray / एक्स-रे
(c) Ultra-violet / परा बैंगनी
(d) Infra-red / इन्फ़रा रेड
Sol. X-ray has the highest energy. Among the given four radiations X-ray has the highest frequency. And Energy E = hv.
Where h = Plank’s constant and
v = frequency.
Q2. Wavelength range of visible light is
दृश्यमान प्रकाश की तरंग दैर्ध्य सीमा कितनी होती है?
(a) 200-900 nm
(b) 600-780 nm
(c) 300-800 nm
(d) 390-780 nm
Sol. Wavelength range of visible light is 390–780 nm.
Q3. A number of images of a flame are seen in a thick mirror, silvered at the back. The brightest image is-
एक ज्वाला की कई छवियों को एक मोटे दर्पण में देखा जाता है, जो पीछे की ओर से चांदी चढ़ा हुआ होता है। सबसे चमकदार छवि है
(a) First image /पहली छवि
(b) Second image /दूसरी छवि
(c) Third image /तीसरी छवि
(d) All image are equally bright /सभी छवियाँ सामान रूप से चमकदार है
Sol. Second Image will be the brightest image
Q4. Light from the sun reached earth in about
सूर्य से प्रकाश पृथ्वी पर लगभग कितनी देर में पहुँचता है?
(a) 2 minutes /मिनट
(b) 4 minutes / मिनट
(c) 8 minutes / मिनट
(d) 16 minutes/ मिनट
Sol. In about 8 minutes light from the sun reaches the earth.
Time = Distance/Speed
Speed of light in air/vacuum = 3 × (10)^8 ms^(-1)
Distance of the earth from the sun = 1.44×(10)^11 m
Q5. Sound travels fastest in
ध्वनि सबसे तेज किस में यात्रा करती है ?
(a) vacuum /वेक्यूम
(b) liquid /तरल
(c) air /हवा
(d) metal /धातु
Sol. Sound travels fastest in metal. Increasing order of speed of sound in different mediums.
Vgas
Sound waves cannot travel through vacuum.
Q6. To hear a clear echo, the minimum distance should be
एक स्पष्ट गूंज/ प्रतिध्वनि सुनने के लिए, न्यूनतम दूरी कितनी होनी चाहिए-
(a) 165 feet / फीट
(b) 165 metre / मीटर
(c) 16.5 feet / फीट
(d) 16.5 metre / मीटर
Sol. To hear a clear echo, the minimum distance should be 16.5 metre.
To hear an echo, time = 1/10 s
Velocity of sound (in air) = 330 ms^(-1)
Time = 2d/(Velocity of sound in air)
⇒ 1/10=2d/330
∴ d = 16.5 metre
Q7. A cut diamond sparkles because of its
एक तराशा हुआ हीरा किस की वजह से चमकता है-
(a) hardness / कठोरता
(b) high refractive index / उच्च अपवर्तक सूचकांक
(c) emission of light by the diamond / हीरे द्वारा प्रकाश का उत्सर्जन
(d) absorption of light by the diamond / हीरे द्वारा प्रकाश का अवशोषण
Sol. Diamonds have a very high refractive index (about 2.42 compared to about 1.5 for glass). The amount of light reflected at an air/other material interface is related to the refractive index charge at the interface and the bigger the refractive index change, the more light is reflected. Thus, diamond reflects large amount of light and therefore, sparkles more.
Q8. Butter paper is an example of …….. object.
बटर पेपर …… .. ऑब्जेक्ट का एक उदाहरण है
(a) a transparent / पारदर्शक
(b) a translucent / पारदर्शी
(c) an opaque / अपारदर्शी
(d) a luminous / प्रकाशमान
Sol. Butter paper is a translucent object as it allows light to pass through it partially, thus not providing clear vision. While, a transparent substance allows light to pass through it completely providing a clear vision. Whereas, an opaque substance is impenetrable to light. On the other hand, luminous objects emit their own light.
Q9. A vibrating body
एक कांपता हुआ शरीर
(a) will always produce sound / हमेशा ध्वनि उत्पन्न करेगा
(b) may or may not produce sound if the amplitude of vibration is low / कंपन का आयाम कम होने पर ध्वनि उत्पन्न कर भी सकता है और नहीं भी
(c) will produce sound which depends upon frequency / ध्वनि उत्पन्न करेगा जो आवृत्ति पर निर्भर करता है
(d) None of these /इनमें से कोई नहीं
Sol. A vibrating body will produce sound which is dependent upon the frequency. Sounds of frequencies less than about 20 vibrations per second (20 Hz) cannot be detected by the human ear. Such sounds are called inaudible. On the higher side, sounds of frequencies higher than about 20,000 vibrations per second (20 kHz) are also not audible to the human ear.
Q10. The special technique used in ships to calculate the depth of ocean beds is
महासागरों की गहराई की गणना के लिए जहाजों में प्रयुक्त विशेष तकनीक है
(a) LASER
(b) SONAR
(c) sonic boom / ध्वनि बूम
(d) reverberation/ प्रतिध्वनि
Sol. SONAR or sound Navigation and Ranging is helpful for exploring and mapping the ocean because sound waves travel farther in the water than do radar and light waves. These also determine the time between the emission of sound pulse and its reception, the transducer can determine the range and orientation of the object.
While, LASER is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Whereas, sonic boom is the sound associated with the shock waves created by an object travelling through the air faster than the speed of sound. On the other hand, reverberation is the prolongation of a sound.
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