Class 12th

Titanium gets its name from the Titans of ancient Greek mythology but this thoroughly modern material is well suited to a huge range of high-tech applications. With the chemical symbol Ti and an atomic number of 22, titanium is a silver-coloured metal valued for its low density, high strength, and resistance to corrosion. Since then, the applications for this metal have grown exponentially, from its use (as titanium dioxide) in paints, paper, toothpaste, sunscreen and cosmetics, through to its use as an alloy in biomedical implants and aerospace innovations. Particularly exciting is the perfect marriage between titanium and 3D printing

Titanium materials are expensive and can be problematic when it comes to traditional processing technologies. For example, its high melting point (1,670?, much higher than steel alloys) is a challenge. The relatively low-cost precision of 3D printing is, therefore, a game-changer for titanium. 3D printing is where an object is built layer by layer and designers can create amazing shapes. This allows the production of complex shapes such as replacement parts of a jaw bone, heel, hip, dental implants, or cranioplasty plates in surgery. It can also be used to make golf clubs and aircraft components.

The CSIRO is working with industry to develop new technologies in 3D printing using titanium. Advances in 3D printing are opening up new avenues to further improve the function of customised body part implants made of titanium. Such implants can be designed to be porous, making them lighter but allowing blood, nutrients and nerves to pass through and can even promote bone in-growth.

Titanium is considered the most biocompatible metal – not harmful or toxic to living tissue – due to its resistance to corrosion from bodily fluids. This ability to withstand the harsh bodily environment is a result of the protective oxide film that forms naturally in the presence of oxygen. Its ability to physically bond with bone also gives titanium an advantage over other materials that require the use of an adhesive to remain attached. Titanium implants last longer, and much larger forces are required to break the bonds that join them to the body compared with their alternatives.
Titanium alloys commonly used in load-bearing implants are significantly less stiff – and closer in performance to the human bone – than stainless steel or cobalt-based alloys.

Titanium weighs about half as much as steel but is 30% stronger, which makes it ideally suited to the aerospace industry where every gram matters.

In the late 1940s, the US government helped to get production of titanium going as it could see its potential for “aircraft, missiles, spacecraft, and other military purposes”.

Titanium has increasingly become the buy-to-fly material for aircraft designers striving to develop faster, lighter and more efficient aircraft. About 39% of the US Air Force's F22 Raptor, one of the most advanced fighter aircraft in the world, is made of titanium. Civil aviation moved in the same direction with Boeing's new 787 Dreamliner made of 15% titanium, significantly more than previous models.

Two key areas where titanium is used in airliners is in their landing gear and jet engines. Landing gear needs to withstand the massive amounts of force exerted on it every time a plane hits a runway. Titanium's toughness means it can absorb the huge amounts of energy expelled when a plane lands without ever weakening. Titanium's heat resistance means it can be used inside modern jet engines, where temperatures can reach 800?. Steel begins to soften at around 400? but titanium can withstand the intense heat of a jet engine without losing its strength.

What is the purpose of using the phrase “the perfect marriage” in the first paragraph?

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Payal Gupta

Contributor-Level 10

The author has specifically mentioned the overall cost of both titanium and 3D printing to indicate how they complete each other in terms of cost. And hence, only the first option could be the best choice here.

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a year ago

The passage given below is followed by four alternate summaries. Choose the option that best captures the essence of the passage.

In 1944, at age 15, Martin Luther King entered Morehouse College in Atlanta under a special wartime program intended to boost enrolment by admitting promising high-school students like King. Before beginning college, however, King spent the summer on a tobacco farm in Connecticut; it was his first extended stay away from home and his first substantial experience of race relations outside the segregated South. He was shocked by how peacefully the races mixed in the North. This summer experience in the North o

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Raj Pandey

Contributor-Level 9

The important keywords in the given paragraph are – race relations, racial segregation and summer in the North. Only C statement captures these key words appropriately and the overall idea of the para. Other options misrepresent the facts.

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a year ago

Class 12th Physics

A student determined Young's Modulus of elasticity using the formula Y = $\frac{M g L^{3}}{4 b d^{3} δ} .$ The value of g is taken to be 9.8 m/s², without any significant error, his observation are as follows:

Physical Quantity	Least count of the Equipment used for measurement	Observed value
Mass (M)	1 g	2 kg
Length of bar (L)	1 mm	1 m
Breadth of bar (b)	0.1 mm	4 cm
Thickness of bar (d)	0.01 mm	0.4 cm
Depression	0.01 mm	5 mm

Then the fractional error in the measurement of Y is:

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Contributor-Level 10

$Y = \frac{M g L^{3}}{4 b d^{3} δ}$

For significant error in Y

$= \frac{Δ M}{M} + \frac{3 Δ L}{L} + \frac{Δ b}{b} + 3 \frac{Δ d}{d} + \frac{Δ δ}{δ}$

$= \frac{1 * 1 0^{- 3}}{2} + \frac{3 * 1 0^{- 3}}{1} + \frac{1 0^{- 2}}{4} + 3 * \frac{0.01 * 1 0^{- 1}}{0.4} + \frac{1 0^{- 2}}{5}$

= 0.0155

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a year ago

Direction for questions: The passage below is accompanied by a set of questions. Choose the best answer to each question.

Class 12th Physics Electric Charge and Field

Direction for questions: The passage below is accompanied by a set of questions. Choose the best answer to each question.

Titanium weighs about half as much as steel but is 30% stronger, which makes it ideally suited to the aerospace industry where every gram matters.

In the late 1940s, the US government helped to get production of titanium going as it could see its potential for “aircraft, missiles, spacecraft, and other military purposes”.

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Payal Gupta

Contributor-Level 10

This is a direct question and all the applications can be inferred from the first paragraph only except there is no mention about buildings.

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a year ago

Class 12th Physics

For a series LCR circuit with R = 100 $Ω$ , L = 0.5mH and C = 0.1 pF connected across 220V – 50Hz AC supply, the phase angle between current and supplied voltage and the nature of the circuit is:

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Vishal Baghel

Contributor-Level 10

$ω = 100 π, R = 100 Ω, X_{L} = L ω = 0.5 * 1 0^{- 3} * 100 π = 5 π * 1 0^{- 2} Ω,$ and

$X_{C} = \frac{1}{C ω} = \frac{1}{0.1 * 1 0^{- 12} * 100 π} = \frac{1 0^{11}}{π} Ω$

Since X_C is approximately infinite, so the phase angle between current and supplied voltage and the nature of the circuit is $\approx 90 °,$ predominantly capacitive circuit.

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For the given circuit the current i through the battery when the key in closed and the steady state has been reached is__________.

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Contributor-Level 10

In given circuit inductor behave as a simple wire so resultant circuit will be

R_ef = 2 + 1 = 3 $Ω$

V = IR

$l = \frac{30}{3} = 10 A$

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a year ago

): The passage below is accompanied by a set of questions. Choose the best answer to each question.

): The passage below is accompanied by a set of questions. Choose the best answer to each question.

The government has made two crucial clarifications on the e-auction process for captive coal blocks in order to make them more attractive to potential bidders. According to the changes introduced by the coal ministry, existing or upcoming power plants that don't have power purchase agreements (PPAs) with buyers of electricity will also be eligible to bid for the coal blocks. Also, the reserve price 100/tonne payable by the successful bidder will be included in the energy charge, which means that fuel cost that will be passed through to consumers will include reserve price along with the actual rate of coal at which the bid has been won. This could translate into bidders being willing to bid more aggressively and still manage to run a profitable business. The minutes of the meeting released by the ministry said: "power projects which do not have PPAs today but would be entering into PPAs (Case I bidding) in future also need to be covered explicitly.”
"Generators without PPAs have been in dilemma for some time. This was because states are unlikely to enter into PPAs with generators that do not have coal linkage and Coal India would refuse to give linkage to generators without PPAs. We have tried to correct the situation by allowing such generators to enter into the auction fray. Apart from the scarcity of coal that has led to more than 15,000 MW of generation capacity not being able to sign coal linkage pact with Coal India, the situation has been exacerbated by the loss-making state-owned distribution companies not shying away from signing pacts with power producers for long-term supply of power because of financial health. While there will not be any deadline in place for such capacity to enter into PPA's they will not be allowed to sell more than 15% of its capacity in the open market. These bidders will also have to pay an additional reserve price for the quantum of coal used for power sold in the merchant market, over and above the reserve price for other generators with long-term PPAs which is 100/ tonne.
The clarification significantly invigorates the auction as there's considerable generation capacity without fully covered fuel supply, and generators can create an additional profit margin between the escalation offered in Case I bidding documents and the actual cost inflation. As regards the reserve price (which is to be paid to the state government) being a pass-through. For merchant power, the reserve price is higher; the new proposal will make sure that there are no extraordinary gains from open market sales. This is a safety feature as bidders would factor in the extra reserve price in their quoted prices."

Which of the following has been considered eligible to bid for the coal blocks after the changes introduced by the ministry?

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Contributor-Level 10

The last option can be inferred from the following lines “According to the changes introduced by the coal ministry, existing or upcoming power plants that don't have power purchase agreements (PPAs) with buyers of electricity will also be eligible to bid for the coal blocks.”

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Class 12th Physics

A square loop of side 20 cm and resistance is moved towards right with a constant speed v₀. The right arm of the loop is in a uniform magnetic field of 5T. The field is perpendicular to the plane of the loop and is going into it. The loop is connected to a network of resistors each of value 4. What should be the value of v₀ so that a steady current of 2 mA flows in the loop

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Class 12th Electromagnetic Induction

Contributor-Level 10

$l = \frac{V_{0} B l}{R} = \frac{V_{0} * 5 * 20 * 1 0^{- 2}}{4 + 1}$

$2 * 1 0^{- 3} = V_{0} * 20 * 1 0^{- 2}$

$V_{0} = \frac{2 * 1 0^{- 3}}{20 * 1 0^{- 2}} = \frac{2}{2} * 1 0^{- 2} = 1 * 1 0^{- 2} m / s$

V₀ = 1 cm/s

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a year ago

An object of mass 'm' is being moved with a constant velocity under the actin of an applied force of 2N along a frictionless surface with following surface profile.

The correct applied force vs distance graph will be:

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