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Rahul J.

Tutor in Physics, Maths, Chemisty etc/

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Physics (Electricity and Magnetism)

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Question:

Why do we use 110 and 220 V? Were these values chosen because they are convenient and are manmade and could have been different, or do they relate to some constant natural law of science? I mean, soft drink cans are 12 oz or 33 cl but this was chosen at random. Cans do not suffer if they are bigger. The minute is 60 sec convention, not a natural law. Maybe electricity travels best in units of 110 V?

Rahul J.

Answer:

We can't think of a physics reason for it. It surely is just random -- in fact more random than the can choice, which is a reasonable size (I finish my can, and don't feel the need for another). You will hear 110, 115, and 120 all quoted as the standard voltage -- I gather that the power company people can't control the voltage that arrives at the house more accurately than that. The value was chosen a long time ago -- probably in the early days of the Westinghouse Corporation (who were the first proponents of AC power distribution) -- and once chosen, we are pretty well stuck with it. All the light bulbs would blow out if the voltage went up to 150, and refrigerator motors will stall and burn out if the voltage goes too low. Flashlight batteries are 1.5 V for a physics reason: it is determined by the amount of energy that is released per electron transferred in the chemical reactions inside the battery. A 9 V battery actually has 6 little cells stacked up inside!

MATLAB

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Question:

Using the plot command for multiple plots, plot y = sin(x) and y = cos(x) on the same graph for values of x defined by: x = 0:pi/30:2*pi.

Rahul J.

Answer:

>> x = 0 : pi/30 : 2*pi; >> plot(x,sin(x),x,cos(x)); >> title(’y = sin(x) and y = cos(x)’); >> xlabel(’x’); >> ylabel(’y’); >> legend(’y = sin(x)’,’y = cos(x)’); >> grid on; >> x = 0 : pi/30 : 2*pi; >> plot(x,sin(x)); >> title(’y = sin(x) and y = cos(x)’); >> xlabel(’x’); >> ylabel(’y’); >> grid on; >> hold on; >> plot(x,cos(x),’r’); >> legend(’y = sin(x)’,’y = cos(x)’); >> ezplot(’(2/3)*cos(pi*x)’,[0,2*pi]); >> title(’High Frequency Cosine Function’); >> xlabel(’x’); >> ylabel(’y’); >> grid on;

C Programming

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Question:

Write a C program to read a value and print its corresponding percentage from 1% to 100% using recursion

Rahul J.

Answer:

#include<stdio.h> //function declaration int RecursvFcnTogetPrcntge(); float Var; unsigned int count=1; float Prcntge; int main() { printf("\nEnter a value to split in percentage: "); scanf("%f",&Var); Var=Var/100; RecursvFcnTogetPrcntge(); printf("\n"); return 0; } int RecursvFcnTogetPrcntge() { if(count==101) { return 1; } Prcntge=Var*count; printf("\n%3d Percent = %.02f",count, Prcntge); count++; RecursvFcnTogetPrcntge(); return 0; }

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