Practice Questions for FMDC (Part 5)

H = I²Rt
Where I²R = electrical power = 100 watts and time = t = 1 hour = 3600 sec
H = 100 x 3600
H = 360000

Like charges repel each other and unlike charges attract each other.
So electron (negatively charged) will move towards the positively charged plate, which is the upper plate in this question.

A good fuse must have minimum resistance because it has to melt whenever a large amount of current passes through it and it must not obstruct the wiring in circuit if it consumes extra electrical power.

6 ohms
Since two resistors of resistance 6 ohms are in parallel so their equivalent (3 ohms : 1/Re = 1/6 + 1/6) is in series in with the third resistor having 3 ohms. That equivalent 3 ohm resistance is series with the third 3 ohm resistor giving an equivalent of 6 ohms.

Remember this mnemonic
BB ROY Goes to Britain Via Germany West
Black = 0 Brown = 1 Red = 2 Orange = 3 Yellow = 4 Green = 5 Blue = 6 Violet = 7 Gray = 8 White = 9
(Capital letters are main focus in mnemonic)
There are four rules to read the color code defined in book.
The color code in our question is
White , violet, red
As first band indicates the first digit of numerical value of resistance and for white we know it is 9 so first digit of numerical value of resistance is 9
Now second band which is violet in color gives the second digit of value of resistance as violet indicates 7 so the second digit is 7
The color code upto this point gives a value of 97
Now look at the third band it is red in color, the third band gives the number of zeroes after the first two digits like in our question the third band is red in color red has value of 2 this means there will be two zeroes after the first two digits. So the final numerical value of resistance is 9700 ohms.

Semi-conductors
Substances having resistivity value between 10^-4 to 10^4 are semi-conductors.

Distance.
Application of Doppler effect, red colored star means longer wavelength which in turn means moving away from the observer.

Remains the same provided mass per unit length or density of the string remains the same.
As f= √(T/m)/2L
f'= √(T'/m)/2L'
Since T’ = 4T and L’ = 2L so
f'= √(4T/m)/4L
f'= (2 √(T/m))/(2×2L)
f^'= 2/2 (√(T/m)/2L)=f

Turns violet gradually
When a star accelerates towards earth the wavelengths constrict and wavelength becomes short and spectrum shifts towards violet portion.

Both ‘a’ and ‘e’
When light travels from one medium to other its frequency remains the same but speed and wavelength changes both have inverse relation with refractive index.
Refractive index of water is more than air which means light will travel slower in water due to its medium density i.e. higher refractive index and it will move faster in air than in water due to lesser value of refractive index of air.
And when light travels from one medium to other there may or may not be a phase change and it does refract making total internal reflection possible.