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 last 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.
/ लोहे की सुई, धीरे से रखने पर पानी की सतह पर क्यों तैरती है?
(a) It will remain under the water, when it will displace more water than its weight / यह पानी के नीचे रहेगी, जब यह अपने भार से अधिक पानी को विस्थापित करेगी
(b) the density of needle is less than that of water / सुई का घनत्व पानी से कम है
(c) due to surface tension / सतही तनाव के कारण
(d) due to its shape / अपने आकार के कारण
Sol. Iron needle floats because its density is less than the density of water.The needle floats upon the surface of the water because it has not broken the surface tension of the water molecules.
Q2. The mass of a star is two times the mass of the Sun. How it will come to an end ? / एक तारे का द्रव्यमान सूर्य के द्रव्यमान का दुगना है। इसका अंत किस रूप में होगा?
(a) Neutron Star / न्यूट्रॉन तारा
(b) Black hole / कालाछिद्र
(c) White Dwarf / व्हाइट ड्वार्फ़
(d) Red Giant / रॅड जायंट
Sol. The mass of a star which is two times the mass of the sun turns into a neutron star.
Neutron stars are very hot and are supported against further collapse by quantum degeneracy pressure due to the Pauli’s exclusion principle. This principle states that no two neutrons (or any other fermionic particles) can occupythe same place and quantum state simultaneously. A typical neutron star has a mass between about 1.4 and 3.2 solar masses ( Chandrasekhar Limit), with a corresponding radius of about 12 km.
Q3. Rain drops fall from great height. Which among the following statements is true regarding it? / वर्षा की बूंदें काफी ऊंचाई से गिरती हैं। इसके बारे में निम्नलिखित में से कौन सा कथन सही है?
(a) they fall with that ultimate velocity, which are different for different droplets / वे उस अंतिम वेग से गिरती हैं, जो अलग-अलग बूंदों के लिए अलग-अलग होते हैं
(b) they fall with same ultimate velocity / वे समान अंतिम वेग से गिरती है
(c) their velocity increases and they fall with different velocity on the earth / उनके वेग में वृद्धि होती है और वे पृथ्वी पर विभिन्न वेग के साथ गिरती हैं
(d) their velocity increases and they fall with same velocity on the earth / उनके वेग में वृद्धि होती है और वे पृथ्वी पर समान वेग से गिरती हैं
Sol.Any mass is attracted to the Earth by the pull of gravity. Gravity accelerates all objects towards the ground at a specific rate. Without any other forces present, the speed of an object in free fall will increase the farther or longer it falls. In general the air resistance on an object depends upon several variables. First, it depends upon the shape of the object. Its shape determines the object’s drag coefficient: the more aerodynamic the shape, the less drag. Second, it depends upon the size of the object;
specifically the cross-sectional area presented to the airflow (perpendicular to the direction of travel). And lastly, it depends upon the speed of the object. At low speeds the object’s resistance is directly proportional to speed, and at higher speeds the object’s resistance is proportional to its speed squared. Most objects falling through the air would be considered to be moving at a higher speed, even though that speed might not be great compared to some velocities.
Q4. On which of the following techniques photostate machine works ? / निम्नलिखित में से किस तकनीक द्वारा फोटोस्टेट मशीन कार्य करती है?
(a) Magnetic Image—Making / मैग्नेटिक इमेज-मेकिंग
(b) Thermal Image—Making / थर्मल इमेज-मेकिंग
(c) Electrostatic Image—Making / एलेक्ट्रोलास्टिक इमेज-मेकिंग
(d) Electromagnetic Image—Making / इलेक्ट्रोमैग्नेटिक इमेज-मेकिंग
Sol. All Electrostatic Copiers work under the premise that a charge of electricity is placed on an Image Drum which has the ability to retain the electric charge much like a capacitor holds its charge but with the ability to hold or release the charge depending on how much light and darkness is applied to the Image Drum. A photocopier (also known as a copier or copy machine) is a machine that makes paper copies of documents and other visual images quickly and cheaply. Most current photocopiers use a technology called xerography, a dry process using heat. Copiers can also use other technologies such as ink jet, but xerography is standard for office copying.
Q5. One Kilowatt hour is equal to— / एक किलोवाट घंटा ______बराबर है।
(a) 3.6 Mega Joule / 3.6 मेगा जूल
(b) 3.8 Mega Joule / 3.8 मेगा जूल
(c) 3.2 Mega Joule / 3.2 मेगा जूल
(d) 4.0 Mega Joule / 4.0 मेगा जूल
Sol. The energy 1 kilowatt-hour (kWh) is 3600000 joules or 3.6 mega joule. In physics, energy is an
indirectly observed quantity that is often understood as the ability of a physical system to do work on
other physical systems. However, this must be understood as an overly simplified definition, as the
laws of thermodynamics demonstrate that not all energy can perform work.
Q6. What is the minimum escape velocity of rocket to be launched into space ? / अंतरिक्ष में लांच किए जाने वाले रॉकेट का न्यूनतम पलायन वेग क्या है?
(a) 5 Km/Sec. / 5 किम/सेकंड
(b) 6 Km/Sec. / 6 किम/सेकंड.
(c) 11 Km/Sec. / 11 किम/सेकंड
(d) 15 Km/Sec. / 15 किम/सेकंड
Sol. On the surface of the Earth, the escape velocity is about 11.2 kilometers per second (~6.96 mi/s),
which is approximately 34 times the speed of sound (Mach 34) and several times the muzzle velocity of a
rifle bullet (up to 1.7 km/s). Escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero. It is the speed needed to “break free” from a gravitational field without further propulsion. A rocket moving out of gravity well does not actually need to attain escape velocity to do so,but could achieve the same result at any speed with a suitable mode of propulsion and sufficient fuel.
Escape velocity only applies to ballistic trajectories.
Q7. Which of the following statements is true when we see ‘rainbow’ ? / जब हम इंद्रधनुष को देखते हैं, तो निम्नलिखित में से कौन-सा कथन सही है?
(a) We face sun and raindrops / हमें सूरज और वर्षा की बूंदे सामने दिखती हैं
(b) The Sun remains behind us and we face raindrops / सूर्य हमारे पीछे होता है और हम वर्षा दिखती हैं
(c) In light rainfall, we face Sun / हलकी वर्षा में, हमें सूर्य दिखता है
(d) The sky remains clear and the sun is at lower position in the sky / आकाश साफ़ रहता है और सूर्य आकाश में नीचे के स्थान पर होता है
Sol. We see rainbows because of the geometry of raindrops. When the sun shines from behind us into
the rain, incident rays of light enter the drop and are refracted inwards. They are reflected from the back
surface of the raindrop, and refracted again as they exit the raindrop and return to our eyes. A rainbow
is an optical and meteorological phenomenon that is caused by reflection of light in water droplets in the
Earth’s atmosphere, resulting in a spectrum of light appearing in the sky.
Q8. How much calorie of energy is released by a boiled egg ? / एक उबले हुए अंडे से कितनी कैलोरी ऊर्जा प्राप्त होती है?
Sol.77-78 calories are released in a large size boiled egg. Boiled eggs are eggs (typically chicken eggs)
cooked by immersion in boiling water with their shells unbroken.
Q9. The splitting of different colours of light in a prism is : / एक प्रिज्म में प्रकाश के विभिन्न रंगों का विभाजन है:
(a) Reflection of light / प्रकाश का परावर्तन
(b) Dispersion of light / प्रकाश का परिक्षेपण
(c) Diffraction of light / प्रकाश का विवर्तन
(d) Refraction of light / प्रकाश का अपवर्तन
Sol. The refractive index of many materials (such as glass) varies with the wavelength or colour of the
light used, a phenomenon known as dispersion. This causes light of different colours to be refracted
differently and to leave the prism at different angles, creating an effect similar to a rainbow. In optics,
dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency, or
alternatively when the group velocity depends on the frequency. Media having such a property are termed
dispersive media. Dispersion is sometimes called chromatic dispersion to emphasize its wavelengthdependent nature, or group-velocity dispersion (GVD) to emphasize the role of the group.
Q10. A boat will submerge when it displaces water equal to its own: / एक नाव तब डूब जाएगी जब वह अपने _____ बराबर जल को विस्थापित कर देगी।
(a) volume / मात्रा
(b) weight / भार
(c) surface area / पृष्ठीय क्षेत्रफल
(d) density /घनत्व
Sol. A boat will float when the weight of the water it displaces equals the weight of the boat and anything
will float if it is shaped to displace its own weight of water before it reaches the point where it will
submerge. Floating of the boat works on the principle of buoyancy force which is an upward force exerted
by a liquid, gas or other fluid, that opposes the weight of an immersed object. In a column of fluid, pressure
increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object
submerged in the fluid, experiences greater pressure at the bottom of the column than at the top. This
difference in pressure results in a net force that tends to accelerate an object upwards.