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## A few selected questions fro CBSE Class 10 Physics Summative Assessment 1

Dear students,

If you are preparing for the CBSE Summative Assessment I for Class X, Give the following questions a try.

If you are not able to solve any of it, please post your doubts as comments to this post. The questions can be discussed here with due explanations.

Make it a practice to solve as much Sample papers and Guess papers as you can before writing the Board Exam.

All the best

1. An electric geyser has the ratings 2000W, 220V marked on it. What should be the minimum rating in whole number of a fuse wire, that may be required for safe use with this geyser? (1Marks)
2. Consider a circular loop of wire lying in the plane of a table. Let the current pass through the loop clockwise. Draw the direction of magnetic field inside and outside the loop. (2Marks)
3. A wire is stretched so as to make its length double. What is the effect on its resistivity and why? (2Marks)
4. Define electric power. Write its SI unit. What is the value of 1 kWh in joules. (2Marks)
5. A torch bulb is rated 3.0V, and 600mA. Calculate its (i) power (ii) resistance (iii) energy consumed if this bulb is lighted for 4 hours.  (3Marks)
6. (i) Differentiate between AC and DC giving two points of difference. (ii) What is the frequency of AC and DC in India? (iii) Draw a graph of current – time for AC and DC. (3Marks)
7. Name and state the law which relates the potential difference in a circuit to the magnitude of current that flows through it. Give its mathematical expression and draw the theoretical graph too. (3Marks)
8. What is electromagnetic induction? State Fleming’s Right Hand Rule. A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is (a) pushed into the coil with north pole entering first? (b) pulled out of the bar magnet? (c) held stationary inside the coil?
9. State Joule’s law of heating. How does the electric fuse prevent fires due to shortcircuit or overloading? A household uses the following electric appliances. (i) Refrigerator of rating 400W for ten hours each day. (ii) two electric fans of rating 80W each for twelve hours each day. (iii) six electric tubes of rating 18W each for six hours each day. Calculate the electricity bill of the household for the month of June if the cost per unit of electric energy is Rs. 3.00. (5Marks)

## Collection of Problems received from Class 12 Physics

These problems were posted by Geena. Hope that we will be able to post the answers to these questions soon; each in a separate post. By the time visitors can attempt to post their answers as comments to this post. (Only selected posts will be published)

Please note that the answers are not published until the Physics teachers are not satisfied with the answers. So, please be patient to get the correct answers rather than approximations in a haste.

If you want real time answers to your queries by a group of Physics Lovers, you can post them at the Physics Fans group with facebook at https://www.facebook.com/groups/askphysics/

1. A series battery of 10 lead accumulators each of emf 2 V and internal resistance 0.25 ohm is charged by a 220 V D.C. mains to limit the charging current a resistance of 47.5 ohm is used in series in the charging circuit. What is a) the power supplied by the mains and b) power dissipated as heat? Account for the difference of powers is (a) and (b).
2. A potentiometer wire has a length L and a resistance Ro. It is connected to a battery and
a resistance combination as shown. Obtain an expression for the potential drop per unit length of this potentiometer wire. What is the maximum emf of a ‘test cell’ for which one can get a ‘balance point’ on this potentiometer wire? What precaution should one take, while connecting this ‘test cell’ , in the circuit?
3. A cell, of emf 4 V and .internal resistance 0.5 Ω, is connected across a load of resistance (i) 7.5 Ω, (ii) 11.5 Ω. Calculate (i) the ratio of the differences in the emf of the cell and the potential drop across the load, and (ii) the ratio of the currents in the two cases.
4. In the figure shown, calculate the total flux of the electrostatic field through the spheres S1 and S2 The wire, AB, shown here, has a linear charge density, λ given by λ = kx where x is the distance measured along the wire, from the end A.
5. A straight wire, of length L, carrying a current I, stays suspended horizontally in mid air in a region where there is a uniform magnetic field B . The linear mass density of the wire is λ. Obtain the magnitude and direction of this magnetic field.
6. Two cells of same emf E, but different internal resistance rl and r2 are connected to an external resistance R as shown. in the figure. The voltmeter V reads zero. Obtain an expression for R in terms of rl and r2. Calculate the voltage across the cell of internal resistance r2. (Assume that the voltmeter V is of infinite resistance).
7. A galvanometer with a coil of resistance 120 ohm shows full scale deflection for a current of 2.5 mA How will you convert the galvanometer into an ammeter of range 0 to 7.5 A ? Determine the net resistance of the ammeter. When an ammeter is put in a circuit, does it read slightly less or more than the actual current in the original circuit? Justify your answer.
8. Figure shows a bar magnet M falling under gravity through an air cored coil C. Plot a graph
showing the variation of induced e.m.f (E) with time (t). What does the area enclosed by the
E – t curve depict ?
9. The electron in the hydrogen atom circles around the proton with a speed of 2.18 x 106 m/s in an orbit of radius 5.13 x 10 -11 m. What magnetic field does it produce at the centre?
10. A proton moves with a speed of 7.45 x 105 m/s directly towards a free proton originally at rest. Find the distance of the closest approach for the two protons. (Given: mass of proton = 1.67 x 10–27 kg and e = 1.6 x 10 –19 C)
11. Figure (a), (b) and (c) show three a.c. circuits in which equal currents are flowing. If the frequency of emf be increased, how will the current be affected in these circuits? Give reason for your answer.

## Which books should be referred for IIT JEE ?

We have received hundreds of questions on the above subject. As the questions continue to pour in, we found it necessary to create a post on it.

IIT JEE is an entrance exam of international repute and IITs are considered at par with MIT by many. So, if you are an IIT aspirant, it is very much essential to prepare well in advance.

In this article we are focusing on Physics only

Know the fundamentals

Knowing the fundamentals is the first step. Learn your daily lessons well. In learning Physics, “Questioning Every Answer is more important than Answering Every Question”

Whenever you learn a new concept, try to get all the doubts clarified. Ask doubts and questions to your teachers. (If they don’t answer you satisfactorily, post them at www.askphysics.com )

Observe your surrounding and try finding examples on what you have learnt. The syllabus and books give you a framework on what to study; but don’t just limit your studies on books and syllabus. Search related information from real life and other sources of reference.

RECOMMENDED BOOKS FOR IIT JEE PREPARATION

The very first book you cannot avoid is the NCERT TEXT BOOK for class XI and XII

These books are designed after thorough research and the exercises are carefully added. Be sure to solve all the exercises including the Additional Exercises

Here are some of the Books you can refer for practicing for IIT JEE

1. Concepts of Physics (by H C Verma)
2. Fundamentals of Physics (by Resnick, Hallidey)
3. University Physics (Zemansky)
4. Problems in Physics (IE Irodov)

By the by, having too much books will be a hindrance. It is better to start with the NCERT books and after mastering all the exercises take up Resnick Hallidey and after clarifying the concepts take up Problems from H C Verma’s concepts of Physics and then go on to IRODOV if time allows.

Wish you all the best.

## Kinematics Problem

In a circus show a clown who is sitting on a post with height,H drops an apple to the ground.At the same time another clown throw an orange vertically upward from ground with speed 11 m/s.If both fruits pass each other after 0.8s, (a) determine the height (b) where do the apple and orange meet? (c) what is the speed of each fruit when they meet each other?

[Asked nur zainun syafiqah ayob]

## Resultant magnetic force

What is resultant magnetic force? can you please explain with an example.

(Shreya)

When a magnetic substance (or a magnet) is placed in a region where there are multiple magnetic fields, the net force due to all of them is called the resultant.

In other words, it is that magnetic force which can effectively replace all other magnetic force acting on it

(Need more explanation? Post as comment to this post for details)

## Can you answer this questions from units and dimensions

“Find the value of 60 joule per minute on a system which has 10cm, 100gm and 1 minute as fundamental units.”

Post your answer as comments. You can also upload a file using the contact page or ask a question page.

## An interesting question on Weight distribution

Leslie asks: ” two persons carry a weight (a coffin in this case) one at each end.

Assuming the coffin is in itself of even weight and that the deceased is of a very heavy torso.

Is the carrier at the end of the head/torso carrying more weight than the one at the feet?”

Have an answer? Please post as comment.

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