## Some Guidelines For students appearing for class XII Physics Board Exams.

### CBSE gives two options for each five marks questions.

You have to be wise while selecting the question for answering. In some cases, one option will carry a "describe the principle construction and working" type and the other may be a combination of small questions.

If you know the answers to the small questions, it is better to choose it, since you will be scoring marks with less time consumption and the marks will be give point wise. It is easy to identify the key points for small questions.

Some general points to keep in mind.

Answer to the point. Avoid unnecessary descriptions and beating around the bush.

Donot repeat the same answer twice or more; you cannot fool the CBSE exam system by that

Draw diagrams neatly using a pencil and scale or other relevant geometrical instruments.

Draw a horizontal line after completing each answer.

Put the main question number within the margin and the subnumbers within the main area.

While solving numerical problems

• Write the data given assigning them suitable symbols

• Put a question mark against the data to be found

• Write the standard equation connecting the knowns and unknowns

• Rewrite the formula with the unknown quantity towards LHS and all other towards RHS and substitute the values in the same order as you have written in the formula.

• The intermediate calculations, logarithms etc maynot be included in the main content area.

• Write the answer with proper unit and double underline the final answer with proper unit.

<hr />

### Derive an expression for current in terms of drift velocity. (Derive I = nAev)

(This is being posted as per request from students)

Consider a conductor of length l and area of cross section A. Let the number of free electrons per unit volume be n. When a pd V is applied, let the drift velocity of electrons be v.

The total no. of free electrons in the piece of conductor = nAl (no. of free electrons per unit volume x volume)

Total charge due to free electrons; q  = nAle

The time taken by this charge to completely traverse the conductor, t =l/v

Therefore, the current in the conductor, I=q/t = nAle/(l/v) = nAev

i.e; I=nAev

### AISSCE Physics 2011 - Sure Shot Questions (Some Suggestions)

Do you know? There are almost always some questions asked from these portions.

• Photoelectric effect (Please learn the full portion)

• Logic gates (please learn full as per syllabus)

• LCR circuit and resonance in AC

• Electromagnetic Spectrum and uses of each of the components

• Any one of "principle construction and working" (Van de graaff generator, Cyclotron, MCG, Dynamo, Transistor amplifier, Transistor as a switch, diode as a rectifier, transistor oscillator)

• Modulation and demodulation (and need for modulation)

## Sunday, February 27, 2011

### Transistor as a Switch

(This is one of the Expected Question for AISSCE Physics 2011)

Explain the action of transistor as a switch.

To answer this question (with proper understanding) you should have an idea of the three regions in the VI characteristics of a transistor. viz; Cutoff region, Active region and the saturation region.

When the input bias of a CE transistor (Vbe) is very low, the transistor does not conduct. So the output voltage (Vce) will be almost equal to Vcc, the output bias voltage.

By increasing the input voltage, the transistor can be brought to saturation region when the transistor will be conducting well. Now the pd across the transistor (Vce) will be very low.

This is the working principle of transistor as a switch.

## Tuesday, February 22, 2011

### Class XII Physics SOME QUESTIONS FROM CBSE 2004 Board Question Paper

Physics 2004 Set 1

2. Two metals A and B have work functions 2 eV and 5 eV respectively. Which metal has lower threshold wavelength?

3. Draw the voltage-current characteristic of a zener diode.

4. A solenoid with an iron core and a bulb is connected to a d.c. source. How does the brightness of the bulb change when the iron core is removed from the solenoid?

5. Peak value of e.m.f of an a.c. source is E0. What is its r.m.s value?

6. An electric dipole of length 4 cm, when placed with its axis making an angle of 60° with a uniform electric field, experiences a torque of Nm. Calculate the (i) magnitude of the electric field (ii) potential energy of the dipole, if the dipole has charges of ± 8 nC.

7. Explain how the resistivity of a conductor depends upon (i) number density ‘n’ of free electrons, and (ii) relaxation time ‘λ’.

8. Two long parallel straight wires X and Y separated by a distance of 5 cm in air carry currents of 10 A and 5 A respectively in opposite directions. Calculate the magnitude and direction of the force on a 20 cm length of the wire Y.

# The physicist who tames lightning

http://physicsworld.com/cws/article/indepth/45092

http://physicsworld.com/cws/article/multimedia/45063

# Spreading the word: why science outreach matters

http://physicsworld.com/cws/article/multimedia/44763

## Thursday, February 17, 2011

### Physics for you magazine "Sample Pages - Examiner's Mind"

Physics for You is an excellent monthly magazine for all those who want to prepare for various Entrance examinations.

You can purchase single edition or subscribe online at http://pcmbtoday.com/index.php?main_page=product_info&cPath=1&products_id=11

## Wednesday, February 16, 2011

Solutions to HC Verma's Concepts of Physics

Part 1

Solutions to HC Verma's Concepts of Physics

Part 2

## Wikipedia says about HC Verma (Harish Chandra Verma)

"Prof. Verma obtained his doctoral degree from Indian Institute of Technology Kanpur in 1980, working under the supervision of G. N. Rao. He then worked as a lecturer and reader at Patna University before joining IIT Kanpur in 1994. Presently he is working on nanocrystalline magnetic materials and alloy systems. He is also interested in Earth Science problems such as meteorites and extinction boundaries."

His book "Concepts of Physics" is a bible for almost engineering entrance exam preparation.

### Revision Test Series for Class XI - Oscillations

PHYSICS TEST PAPER (OSCILLATIONS)

Time : 1 ½hr M. Marks: 40

• Q.Nos 1 to 5 carries 1 mark each

• QNos 6 to 10 carry 2 marks each

• QNos 11 to 15 carry 3 marks each

• QNos 16 – 17 carry 5 marks each

1.      What is periodic motion?

2.      How will the time period of a simple pendulum change if its length is doubled?

3.      Two identical springs of force constant k each are connected in series. What will be the equivalent spring constant?

4.      What is the time period of a simple pendulum in a satellite orbiting around the earth?

### Verified Links for Studying Waves online

http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/waves/

http://revise-physics.net/IGCSE/pdf/P9Waves.pdf

http://www.gcse.com/waves.htm

http://www.physicsclassroom.com/Class/waves/

http://library.thinkquest.org/10796/

Copy - paste the above links on address bar to study waves in detail

### IIFT Records 100% Placements; Highest Domestic Salary Was Rs 15.51 Lakhs

The campus placements of the Indian Institute of Foreign Trade (IIFT) held in the Capital recently were successful with a 100% placement record. A total of 96 companies participated in the event and the Finance sector emerged as the largest recruiter for the 2011 batch. A 10% increase has been recorded in the average domestic salary (which was Rs 11.6 lakh) and students got job offers from across the world such as in Europe, Singapore, Middle East and Africa. The highest international package offered at the campus was \$150,000 by Olam International and the highest domestic package offered was Rs 15.51 lakh.

### IE University Announced A New Bachelor of Laws Programme With Focus On Business

IE University in Spain is launching a new undergraduate law programme which is very different from the traditional courses on offer. Currently, it offers four specializations: corporate laws, environmental laws, EU laws, and transnational laws. The students will also have an option to take up a dual-degree programme called the Bachelor of Laws and Business Administration. The course will be offered in both English and Spanish and will be offered at the Madrid and Segovia campuses of the varsity from September 2011.

### NIIT Enters Into Alliance With Zend Technologies For PHP Training‎

NIIT, a leader in the IT training space and Zend Technologies, the PHP Company have together launched a PHP training and certification program that will extend across more than 450 centers in India. The new program aims to cultivate a talent pool of PHP experts and Zend Certified Engineers in India to cater to the demands of the enterprise IT organizations and system integrators delivering application development projects, especially in the U.S. and Europe.

## Tuesday, February 15, 2011

### DERIVATION OF CELLS IN SERIES AND PARALLEL

jaipreet singh asked: "can you please tell me the DERIVATION OF CELLS IN SERIES AND PARALLEL?"

Answer: I am posting here the simplified treatment to calculate the current in a circuit with combination of cells.

In this derivation it is assumed that all cells have the same EMF and same internal resistance.

CELLS IN SERIES

Consider n identical cells of emf E and internal resistance r connected in series across an external resistor of resistance R.

The total internal resistance = nr (since the internal resistances come in series)

The total resistance in the circuit = nr+R

The total emf = nE (since the emfs add up in series circuit)

Therefore, the current in the circuit;$current =\frac{Total Emf}{Total resistance}$
$I=\frac{nE}{nr+R}$

PARALLEL COMBINATION OF CELLS

Consider m identical cells of emf E and internal resistance connected in parallel across an external resistor of resistance R.

The total emf in circuit = E (Since each cell has the same emf and they are in parallel)

The net internal resistance = r/m (since the cells are in parallel, their resistances are also in parallel. If m identical resistances are in parallel, the effective resistance is r/m)

The total resistance in circuit = R + r/m

Therefore, the current in circuit;$Current = \frac{Total EMF}{Total Resistance}$
$I = \frac{E}{mr+R}$

MIXED COMBINATION OF CELLS

Consider a combination of m rows of n cells each. The emf of each cell is E and the internal resistance of each cell is r. This combination is connected across and external resistance R.

The total EMF = nE

The net internal resistance = nr/m

The total resistance in circuit = R + nr/m

The current in circuit; $Current = \frac{Total EMF}{Total Resistance}$
$I = \frac{nE}{\frac{nr}{m}+R}=\frac{nmE}{nr+mR}$

## Monday, February 14, 2011

### Physics Songs

One student requested that he was given an assignment on composing a song based on the laws and principles of Physics. So, I am posting some links here to various sites which posted Songs based on Principles of Physics.

### Valentine's Day Physics Contest !

What Physics in Valentine's Day Contest

Share what Physics you applied on Valentine's Day.

Only approved entries will be published.

Best of the entries received will get free registration card/login card worth Rs. 995/- for www.exam2home.com - An online portal for exam preparation.

The entries must be genuine and should contain concepts from Physics.

## Wednesday, February 9, 2011

### Educational News Update

Visa Relief To Tri Valley University’s Students In US

Responding to India’s strong reaction to how US authorities have been treating Indian students enrolled at the ‘sham’ Tri-Valley University in California, the US Immigration and Customs Enforcement (ICE) hinted that it would reinstate the visas of victimized Indian students through the I-539 form. I-539 form is used by the US Citizenship and Immigration Services (USCIS) to extend the visas and change immigration status of foreign nationals visiting the US. However, the request for visa extension or change of immigration status will only be considered on a case by case basis.

B-schools Plan Legal Action To Seek Reprieve From New AICTE guidelines

Over 200 management institutes across India are in discussions to approach the Delhi or Bombay High Court as a consortium and seek reprieve from recent guidelines issued by the All-India Council for Technical Education (AICTE). Among other things, AICTE had asked for common entrance tests for all PGDM programmes across the institutes, not to start admission process before March 31 in any academic year, and the institutes to seek approval of their course from their state panel.

Post-Study Employment Curbs In The UK Can Hit Number Of Indian Students Going There For MBA

In the wake of growing unemployment in Britain, the UK government abolished the visa that allowed Indian and non-EU students to work in the UK for two years after the completion of their courses. However, the London-based Association of MBAs holds a view that the move will hit the number of international students from India and elsewhere enrolling for MBA in the country. India and China are the biggest markets for international students for the UK and restricting their access to jobs market after studies can threaten future viability of the business education industry. MBA courses have high fees and international students are a good source of income for UK universities struggling for funding.

US Varsities Assessing Asian Aspirants Holistically; Reducing Focus on Test Scores

US universities are now judging higher education aspirants from India and Asia more holistically and trying to reduce their dependence on entrance test scores such as SAT, GMAT and GRE. They are also taking exceptional credentials of the student, their professional experience, insightful essays, social work and industry contacts into account while accepting students into their academic programmes.

CBSE To Offer Courses In Media, Films, Geospatial Studies, And Hospitality

After the huge success of introducing vocational courses during the last session, the Central Board of Secondary Education (CBSE) is all set to introduce courses in media, films, geospatial studies and food & beverages in 11,000 schools in India and abroad affiliated to it. The courses will be introduced in class XI from the academic session 2010-11 on pilot basis.

India Needs Regulatory Mechanism For Education Agents Working For Foreign Universities

Fake Indian education agents, working for lesser-known foreign universities, are to blame for students falling victim to fake universities like Tri-Valley University (TVU) in the US. If the Indian students had sought admissions through proper channels, they could have avoided being caught up in the visa and immigration scam at TVU, experts say. The Ministry of Overseas Indian Affairs will introduce a new bill in the coming session of Parliament that will make it mandatory for all education agents to register with the government.

Samsung Launches IT And Mobility Solutions For Educational Institutes In India

Samsung India Electronics has come up with some novel display solutions and customized applications for the education segment. The Smart Classroom offers large displays for showcasing digital content in the classroom; the Smart Teacher will be used to maintain course curriculum, plan attendance, and access an institute’s intranet for content; the Smart Student offers access to course syllabi and digital content over intranet; and the Smart School solution for professional course students, which includes notebooks and thin clients.

London Metropolitan University Professor Advocates Friendly Relations Between India And China

Prof. Mark Bickerton from London Metropolitan University suggested that India should improve its relationships with neighbouring countries, especially with China, in mutual interest of both the Asian Countries that are rapidly growing into powerful nations. He was speaking as a guest lecturer at the Institute of Management Studies (IMS), Noida on the topic 'Is 21st century Asian?'.

Students Suspended For Defaulting On Attendance Go On Rampage

MVLU College and Chinai College of Commerce, Andheri in Mumbai suspended about 320 students for defaulting on attendance. National Students' Union of India (NSUI), Yuva Sena and MNS students' wing are protesting against the move that has turned violent. The identity cards of these students have been confiscated and the hall tickets of 45 final year students have been withheld by the college authorities. Without the hall tickets, these students will not be able to appear for their exams that are to be held on February 14, and February 24.

Health Ministry To Open New Medical Colleges In India

The Health Minister Ghulam Nabi Azad announced on Friday that the Indian government will soon introduce 4,000 seats in medical colleges already run by the government as well as open new colleges to give an impetus to medical education in India. The ministry will also open 269 new nursing colleges to strengthen the paramedical structure in the country.

IIM-A Planning To Launch Academic Programmes In Dubai Or Singapore By 2013

The Indian Institute of Management, Ahmedabad (IIM-A) is looking to rent campuses in Dubai or Singapore or both, by 2013. Earlier, the institute had been hesitant to set up a campus abroad because of the shortage of faculty. IIM Bangalore (IIM-B), first of the IIMs to conceive of an international footprint in Singapore six years ago, said that it is still figuring out the demand for its MBA programmes internationally.

Gujarat Technological University (GTU) Is All Set To Overhaul Education System In Its Polytechnics

Gujarat Technological University (GTU) has made it mandatory for all its 86 polytechnic colleges to teach for at least 90 days in a semester, as per UGC guidelines; and use the 'case study method' that would initiate interaction and discussions between students. GTU will keep track of academic sessions in each of its diploma colleges through a monthly report system.