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# Monthly Archives: February 2014

## IMPORTANT DERIVATIONS FROM OPTICS FOR CBSE STUDENTS CLASS XII AISSCE

Please practice these derivations from Optics to excel in Physics for Class 12 CBSE Physics

## Previous years Board Questions from Optics

Find below a collection of questions asked in Board Examination (CBSE) from the chapter Optics. Optics is the chapter having the highest weightage of marks. So, learning this chapter (optics) increases your chances of passing the exam.

## LEARN COMMUNICATION – CBSE PHYSICS FOR CLASS XII ONLINE

Here’s an online study guide to Communications, the last chapter in CBSE Physics for class XII. Hope that the guide will help you score better marks in your AISSCE 2014

Here’s a worksheet for the chapter Communication Systems ## Solar Power

Suppose a PVC solar cell converts or absorbs 30% of the electromagnetic radiation which falls upon it, where I understand that “Gamma rays” or the such simply pass through it, would it not be so that a large portion of the 70% not converted, if directed to yet another PVC, could this second PVC convert 30% of the reflected 70% which the first PVC did not convert? I believe the answer is “Yes, for the most part” which would than imply that the unabsorbed portion of the second pass could be directed again to a third PVC.

Is this correct? ## Force and acceleration – Can force be exerted without acceleration?

I am not able to understand this and I couldn’t think of a better example. i repeat. its just an example. if i punch someone’s face with my arm having constant velocity, it will mean that the acceleration of my arm is zero. F=ma, therefore force exerted by my arm is zero. Now if the force applied is zero the why does the person whom i punched experiences pain….. please help… thanks… It’s not whether your hand is moving with constant velocity, bu what happens to your hand after hitting the face of the opponent. The face resists the motion of your hand the momentum of your hand is imparted/shared to the face. And there is (-)acceleration to the hand and causes a force to be exerted on the face. The momentum imparted to the face will be responsible for the damage caused. ## Relationships and graphs

Suppose we consider an object identified with three parameters – call them A, B and C – and that each
parameter is dependent somehow on some other independent parameter called w. The relationships between A, B and C are determined by a set of rules. In this case, the rules are:
1. On a graph of B vs. w, the slope of B is given by the rate of change of A with respect to w. Further,
the value of B for any particular value of w is given by the area under the plot of A vs. w.
2. On a graph of C vs. w, the slope of C is given by the rate of change of B with respect to w. Further
the value of C for any particular value of w is given by the area under the plot of B vs.w.
3. The particular value of B at w = 0 is given by B^0 and the value of C at w = 0 is given by C^0.
Our task is divided into two parts. Using only the properties of the graphs mentioned in the rule set, we are to first show that the symbolic relationship for the behavior of B vs. w and C vs. w, for the conditions that B^0 =0 and C^0 =0 is given by B = A W and C = 1/2 A w^2. Note carefully that the results to be proven must involve properties of the graphs and not simply algebraic manipulations.
The second step is to relax the conditions on B^0 and C^0 to be any non-zero value and to show the relationships to then be B = B^0 + A w and C = C^0 + B^0 w + 1/2 Aw^2. Once again, note carefully that the results to be proven must involve properties of the graphs and not simply algebraic manipulations.

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