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Edexcel PHYSICS Doubts

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dk bose:
1)A capacitor charges through a 0.22 M ohm resistor. Calculate the capacitance if the time taken for it to reach full charge is 5 minutes.

2)A 47*10^-6 F capacitor is charged to a potential difference of 15V and then discharged through a 100 k ohm resistor. How long does it take for half of the energy stored in the capacitor to have dissipated in the circuit?

3)Mains-operated power supplies have large-value capacitors to help keep the output voltage constant. In
a full wave rectified supply, without a capacitor the output falls to zero every 10 ms. If the output must be
maintained at a value at least 90% of its maximum value when a load of 1.0 k ohm is connected to the output
terminals, show that the minimum capacitance needed in the power supply circuit is about 100*10^-6F.

astarmathsandphysics:
1) A capacitor always takes an infinite time to be fully charged.

astarmathsandphysics:
The attached solution was done on some random piece of paper

dk bose:
1)Explain why a ship's plimsoll line has a mark for fresh water which is higher on the hull than the mark for salt water(assume density of salt water=1100kgm-3).

2)A ball bearing of mass 180g is hung on a thread in oil of density 800kgm-3.Calculate the tension in the string ,if the density of the ball bearing is 8000kgm-3.
3) Give three examples of objects which are designed to reduce the amount of turbulent flow of air or water over them.
4)Explain these poetic observations of the flow of a lake district stream:In the gentle time of a late summer, a creek over boulder flowed smooth.As autumn fell,floating leaf after leaf skipped round the rock,chasing like giddy schoolgirls playing 'Follow the leader'. In winter's depth,all frozen stood,ice on stone,stone on ice.The bright thaw springs a maelstrom,water currents churning and swirling as drunken Maypolers.
5) How and why would holding a swimming competition in a warmer pool affect the times achieved by swimmers?

astarmathsandphysics:
1)cos fresh water is less dense than salt water so sho upthrust is less so ship is lower in the waer
2)V=mass/density=0.180/8000=2.25*10^-5 m^3
Upthrus=weight of oil displaced =density*volume*g=800*2.25*10^-5=0.018g
tension=wieght-upthrust=0.180g-0.018g=1.5876N
3)fins/wings/shark skin
4)is this an english question?
5) would be quicker since water molecules move faster.

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