RRB ALP 2019 Previous Year GK Questions with Answers

The correct answer is B, Friction. Brakes work on friction: a lining is pressed against a moving drum or disc, and the rubbing force slows the wheel down. Friction is the force that opposes motion between two surfaces in contact. In a drum brake the shoes push outward against the inner face of the drum, while in a disc brake the pads grip a rotating disc from both sides; in each case the kinetic energy of the vehicle is turned into heat, which is why brakes grow hot on a long downhill run. The friction between the tyre and the road then stops the vehicle itself, so a smooth or wet road lengthens the stopping distance. Option A is wrong because vibration only shakes a body and cannot take away its energy in a controlled way. Option C is wrong because suction is a pressure difference; a vacuum booster only helps the driver press the pedal, it does not stop the wheel. Option D is wrong because dragging is not a physical principle. Exam tip: brakes turn kinetic energy into heat through friction.

The correct answer is C, Boron. Boron has three electrons in its outermost shell, so it is a trivalent element and is used as a p-type dopant. When a trivalent atom such as boron, aluminium, gallium or indium is added to silicon or germanium, it can form only three covalent bonds with its four neighbours, so one bond is left incomplete. That empty place is called a hole, it behaves like a positive charge carrier, and the doped crystal becomes a p-type semiconductor in which holes are the majority carriers. Adding a pentavalent atom instead leaves a free electron and gives an n-type semiconductor. Option A is wrong because arsenic has five valence electrons and is pentavalent. Option B is wrong because antimony is also pentavalent and is used for n-type doping. Option D is wrong because phosphorus has five valence electrons and donates an electron to the crystal. Exam tip: trivalent dopants such as boron, aluminium, gallium and indium give p-type material, while pentavalent ones such as phosphorus, arsenic and antimony give n-type.

The correct answer is C, Anti-lock braking system. ABS stands for anti-lock braking system, a safety device that keeps the wheels from locking during hard braking. Sensors at the wheels watch how fast each one is turning, and when a wheel is about to stop turning the control unit releases and applies the brake pressure many times a second. Because the wheels keep rolling, the tyres hold their grip on the road, so the driver can still steer while braking hard and the vehicle usually stops in a shorter distance. A locked wheel simply skids and goes wherever it was already going. ABS is now required by law on cars and on larger two-wheelers in India. Option A is wrong because 'avoid brake system' is not a term used for any vehicle part. Option B is wrong because 'actual brake system' has no meaning in engineering. Option D is wrong because an automatic braking system is a different feature in which the vehicle applies the brakes by itself to avoid a crash. Exam tip: ABS prevents wheel lock and keeps steering control; it does not replace the brakes.

The correct answer is A, 2. A centre-tap full wave rectifier needs two p-n junction diodes, one for each half of the input cycle. The secondary winding of the transformer is tapped at its middle, so its two halves give equal voltages of opposite sign. During one half cycle the upper diode conducts and during the next half cycle the lower diode conducts, and both send current through the load in the same direction, so the output has two pulses in every cycle. That is why a full wave rectifier gives a higher average output and a lower ripple than a half wave one. The other way to build a full wave rectifier is the bridge circuit, which uses four diodes but needs no centre tap. Option B is wrong because one diode makes a half wave rectifier that uses only half of each cycle. Option C is wrong because four diodes are used in a bridge rectifier. Option D is wrong because six diodes are used in a three-phase full wave rectifier. Exam tip: half wave 1 diode, centre-tap full wave 2, bridge 4.

The correct answer is D, 0.7 V. A silicon diode in forward bias drops about 0.7 volt across itself, whatever the supply voltage is. This value is the barrier or knee voltage of a silicon p-n junction: current begins to flow only after the applied voltage crosses about 0.7 V, and after that the drop across the diode stays near 0.7 V while the rest of the supply appears across the resistor. Here 12 V minus 0.7 V, that is 11.3 V, falls across the 240 ohm resistor and fixes the current in the circuit. A germanium diode has a lower knee voltage of about 0.3 V. Option A is wrong because 1.5 V is the voltage of a dry cell and has nothing to do with the junction. Option B is wrong because half the supply would appear across the diode only if it behaved like a resistor of the same value. Option C is wrong because the full 12 V appears across the diode only when it is reverse biased or the circuit is broken. Exam tip: silicon 0.7 V, germanium 0.3 V.

The correct answer is B, Cambodia. Angkor Wat stands near Siem Reap in Cambodia and is the largest religious monument in the world. It was built in the early twelfth century by King Suryavarman II of the Khmer empire as a temple of Vishnu, and it later became a Buddhist place of worship. The temple faces west, is ringed by a wide moat, and its towers are shaped like lotus buds; UNESCO put the whole Angkor complex on the World Heritage list in 1992. Angkor Wat also appears on the national flag of Cambodia, which is the only national flag in the world that carries a building. Option A is wrong because Vietnam is known for Ha Long Bay and the My Son Cham temples. Option C is wrong because Thailand's best known temple is Wat Phra Kaew in Bangkok. Option D is wrong because the Philippines is known for its rice terraces and baroque churches. Exam tip: Angkor Wat, Cambodia, built by Suryavarman II and shown on that country's flag.

The correct answer is C, spam. Unwanted bulk messages sent to many people to advertise something are called spam. Spam usually arrives as e-mail, but the same word is used for unwanted SMS, blog comments and social media messages. Mail services run spam filters that study the sender, the subject line and the words used, and move such mail to a separate Spam or Junk folder so that it never reaches the inbox. Spam that pretends to come from a bank and asks for passwords or card details is called phishing, and a person who sends spam is a spammer. Option A is wrong because a virus is a harmful program that copies itself into other files and damages data. Option B is wrong because unzip only means opening a compressed file such as a .zip archive. Option D is wrong because a URL is the address of a web page. Exam tip: unwanted bulk mail is spam, while fake mail that asks for your details is phishing.

The correct answer is A, Nagaland. The Hornbill Festival is held every year from 1 to 10 December at Kisama Heritage Village near Kohima, the capital of Nagaland. It is called the "Festival of Festivals" because all the major Naga tribes come together in one place to show their dances, songs, crafts, food and traditional games. The Nagaland government started it in 2000 to promote tourism and protect Naga heritage. It is named after the hornbill bird, which appears in many Naga folk tales and in their traditional headgear. The festival opens on 1 December, Nagaland's Statehood Day, as the state was formed on that day in 1963. B is wrong because Sikkim is known for Losar and Saga Dawa. C is wrong because Andhra Pradesh is known for Sankranti. D is wrong because Jammu and Kashmir is known for events such as the Tulip Festival in Srinagar. Exam tip: Hornbill = Nagaland (1 to 10 December, Kisama), Sangai = Manipur, Wangala = Meghalaya, Losar = Sikkim and Ladakh.

The correct answer is D, Volt. Potential difference is the work done to move a unit charge between two points, and its SI unit is the volt. V = W/Q, so 1 volt = 1 joule per coulomb. It is measured with a voltmeter, which is always connected in parallel across the part of the circuit being tested. The unit is named after Alessandro Volta, the Italian scientist who made the first electric battery, the voltaic pile. Household supply in India is 230 V, while a pencil cell gives 1.5 V. A is wrong because the ampere is the unit of electric current, measured with an ammeter joined in series. B is wrong because the tesla is the unit of magnetic field strength (magnetic flux density). C is wrong because the coulomb is the unit of electric charge; one coulomb is the charge of about 6.25 × 10¹⁸ electrons. Exam tip: Current = ampere, Charge = coulomb, Potential difference = volt, Resistance = ohm, Power = watt, Energy = joule.