|
Question 1. In recent years astronomers have discovered that dwarf galaxies such as NGC 5234 are far more common than previously supposed. Moreover these galaxies are very different from their bigger cousins: they spend billions of years in a dormant state, then erupt in furious short-lived bursts of star formation. Starbursts also occur in large galaxies, but the radiation from those bursts is usually obscured by other galactic emissions; only in dwarf starburst galaxies can researchers get a clear look at these phenomena. These galaxies hold clues to the early history of the universe _ they are relics of an ancient time, composed of material that has changed little since the big bang.
What causes starbursts in dwarf galaxies, and why are they so important to astronomers? To answer these questions we must examine the mechanics of star formation. Astronomers know that stars have been forming for almost the entire duration of the universe. Our own galaxy, the unremarkable larger spiral called the milky way contains at least 100 billion stars. Star formation in the Milky Way is a slow and steady process involving the contraction of vast clouds of interstellar gas and dust. Every year, on an average about one solar mass of gas and dust (that is an amount equal to the mass of our sun) turns into new stars.
In contrast, a starburst is a relatively brief period _ from one million to 20 million years _ during which the rate of star formation is much higher than average. Astronomers have observed galaxies in which the rate is 100 times higher than the Milky Way's. We know this to be a short-lived stage because if it had been going on for more than hundred million years the galaxy would have run out of the gas from which the stars are made. The increased star formation rate causes a dramatic rise in the galaxy's brightness. Because starbursts are brief, they are dominated by the radiation from hot young stars of 20 solar masses or more, which have lifetimes of only a few million years. A strong starburst can be almost as bright as a quasar, the most luminous object in the universe. Because a star burst's luminosity is concentrated in the radio and infrared parts of the spectrum, the phenomenon has been recognised and studied only in the past 20 years as new telescopes and satellites have allowed scientists to observe these wavelengths
Many astronomers believe that starbursts play a pivotal role in galactic evolution and the creation of star clusters. For this reason scientists are eager to know what triggers these sudden episodes, how they proceed and what turns them off. These questions may be easier to answer in dwarf galaxies which hold 100 million or fewer stars, than in the large spirals such as the Milky Way and M83
1. According to the author the study of starbursts is easier in dwarf galaxies because
1. they are relatively stable and have changed little since their inception.
2. their radiations are easier to isolate in these galaxies
3. they are smaller and composed of relatively fewer stars.
4. they alone contain answers to questions about the mechanics of star formation.
5. starbursts are more intense and frequent in these galaxies
Answer : 3
Explanation :
The last sentence of the passage holds the answer to this question. This states clearly dwarf galaxies hold fewer stars and so a study of these will yield an answer to many of the astrologers' questions. So option 3 is the correct answer.
2. Astronomers according to the author, are keen to study starbursts because
(B)
(C)
(D)
(E)
1. starbursts are intriguing phenomena that have not yet been studied.
2. this is the process by which star formation takes place.
3. it could contain evidence of the big bang.
4. the radiations from these could be potentially useful to humans.
5. these could help understand how early galaxies were formed.
Answer : 5
Explanation :
The first sentence of the last paragraph states clearly that starbursts play an important role in galactic evolution and formation of star clusters. Option 5 gives us the correct answer.
3. To support the statement that starbursts are a short-lived stage, the author,
1. points to data from astronomical observations
2. argues that it is a logical consequence of the rapid rate of star formation
3. proves they are dominated by hot young stars
4. argues that a longer stage cannot be materially sustained.
5. Cites the work of various astronomers.
Answer : 4
Explanation :
The third sentence of the third paragraph gives us a reason for this: the author states that the galaxies would have run out of the gas out of which stars are made if they had been going on for a longer period. So option 4 is the correct answer.
Question 12. Measurement ranks as one of our oldest skills. Many of the questions people ask every day begin with "How many?" or "How much?" A person may ask a friend, "How many brothers and sisters do you have?" or, "How much do you weigh?" The answers to both questions use numbers. But the first question is answered by counting, and the second by measuring. Each child in a family is a whole person and must be counted, not measured. But a person's weight must be measured, and this is done by standing on a scale.
Almost everyone uses measurement daily. The food we eat, the clothes we wear, the work we do, and many of the games we play involve measurement. For example, shoppers buy meat by the kilogram and cloth by the meter. Many workers are paid by the hour. An athlete who runs 100 meters in the shortest time wins the race.
People also use measurement to help them understand one another and to work together easily. A boy could write to someone living far away and describe himself as tall and heavy. But it would be better if he described himself as 137 centimeters tall and weighing 40 kilograms. In the same way, a carpenter building a house can order a door that measures 76 centimeters wide and know it will fit the opening allowed for it.
Every measurement involves two things: (1) a number and (2) a unit. A number by itself is not a measurement. There would be no point in saying that a stick has a length of 6. No one would know whether the stick was 6 centimeters or 6 meters long. But if someone described the stick as being 6 centimeters long, then the measurement would have meaning.
There are two major systems of measurement: (1) the imperial system and (2) the metric system. The measurement units in each system are related to one another. The imperial system of measurement started in about the 1200's, though its units may be traced back even earlier. Most nations--and all scientists--use the metric system. The official name of this system is the Systeme International d'Unites (International System of Units).
To make accurate measurements, people have invented such measuring tools as clocks, scales, tape measures, thermometers, and other devices. Measurement with tools involves comparing the object or event being measured with the units marked on the tool. For example, a ruler placed beside a pencil shows the number of centimeters and millimeters equal to the length of the pencil.
Most measurements involve reading some kind of scale. The problem is that no matter how many subdivisions the scale has, the object being measured is likely to fall between two of them. As a result, every measurement can only be an approximation. A measurement may come close, but it never matches the scale perfectly. Without a magnifying lens, for example, a ruler is accurate only to within a half millimeter. But simple measurements within a fiftieth of a millimeter can be made with an instrument called a micrometer caliper.
Measuring tools include a wide variety of devices. Gauges and meters measure such items as liters of petrol or cubic meters of natural gas. A kilowatt-hour meter measures electricity. A speedometer measures the speed of a car or other vehicle, and an odometer records the distance traveled by the vehicle. Other devices measure the volume of such substances as petroleum in barrels.
1. The primary purpose of the passage is to
1. make out a strong case for the superiority of the imperial system of measurement over the metric system on the grounds of accuracy
2. make a detailed list of all the devices that are in general use today for the accurate measurement of objects, distances and speeds
3. briefly explain the importance, function, systems and types of measurements that are used in everyday life.
4. show the various means that were employed by people after the 1200s to measure.
5. describe the various situations in which human beings need to measure and count in their everyday activities.
Answer : 3
Explanation :
In this passage, the author mainly talks about measurement, its importance in our lives, the daily usage of it. So the answer is option 3.
2. According to the passage, in order to measure anything
1. it is necessary both to count and use devices within either system of measurement
2. a unit of one object has to be contrasted with a unit of another object
3. a scale called the micrometer calliper has to be used with great precision
4. it is first necessary to accept that all measurements are only approximations
5. both a number and a unit of measurement are required
Answer : 5
Explanation :
Line 1 of para four clearly directly gives the answer. The correct answer is option 5.
3. Most measurement is only an approximation because
1. it involves both a number and a unit and it is unlikely that both of them can be accurate enough
2. the object being measured is likely to fall between the calibrations of the scale or device that is used to measure
3. the devices used to measure objects cannot be made to fit all the possible objects that have to be measured accurately
4. accurate measurement in almost all the cases involve the use of powerful optical instruments like magnifying glasses which are not commonly available
5. most people who measure are not trained in the use of numbers, units and devices used to measure objects
Answer : 2
Explanation :
The answer is the second line of para 7. It is a direct answer. The correct choice is therefore option 2.
Back to Articles Section
|
