R < r
R = r
R = 2r
R > r
Correct answer is B
Power = I\(^2\)R
= \((\frac{E}{R + r})^2 R\)
To get point of maximum power transfer, we take the derivative and equate it to 0.
\(P = E^2 (\frac{R}{(R + r)^2})\)
\(\frac{\mathrm d P}{\mathrm R} = E^2 (\frac{(R + r)^2 - 2R(R + r)}{(R + r)^4})\)
= \(E^2 (\frac{(R + r)[(R + r) - 2R}{(R + r)^4})\)
\(\frac{\mathrm d P}{\mathrm d R} = E^2 (\frac{r - R}{(R + r)^3})\)
Maximum power is gotten when r - R = 0 i.e. r = R.
A drop of petrol makes a finger colder than a drop of water would because?
petrol takes its latent heat of veporization from the finger
petrol takes its latent heat of fusion from the finger
water is more viscious than petrol
water has higher surface tension dan petrol
Correct answer is A
No explanation has been provided for this answer.
the glass will break
the glass will shrink
the liquid will rise up in the stem
the liquid will go down in the stem
Correct answer is D
No explanation has been provided for this answer.
The thermos flask is designed to?
prevent heat loss or gain by conduction, convection amd radiation
store hot tea or water
prevent heat gain by conduction, convection and radiation
prevent head lost conduction, convention and radiation
Correct answer is A
No explanation has been provided for this answer.
1.05 x 103s
1.05 x 105s
1.05 x 102s
1.05 x 104s
Correct answer is A
Power of heater = lvt = 2 x 240 x t
heat required to boil the water = Mct = 2.5 x 4.2 x 103 x (100.52) = 2.5 x 4. 2 x 103 x 48
2 x 240 x t = 2.5 x 4.2 x 103 x 48
∴ t = (2.5 x 4.2 x 103 x 48)/2 x 240
= 1050s or 1.05 x 103s