Physics, Chemistry and Biology: Post your doubts here!

[eureka!]

Hey, can sm1 explain me fleming's rule?

Left or right hand?

 

[pyaparus]

Left or right hand?

Left

 

[Ahmed the Seeker]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w10_qp_33.pdf
question 2 please I struggled alot with it.

 

[eureka!]

eureka!

Q) Explain why energy losses in the transmission cables are lower when the voltage is
high.


Ans) high voltage means) low(er) current (but V is directly prop. to R!)
for given supply power
(low(er) current means) less heat/thermal energy (generated in cables) OR P = I2R (?)
for given resistance (of cables)
cables heated by current

Explain...

Suppose you wanna send 4 MW of power through a cable of 4 Ω.
P=IV. You've got many options, e.g. sending 10A at 400 000 V, 160A at 25000 V, etc.
Now, what would the p.d. across the wire be if you deploy the 25 000 V solution?
V=IR; 160 x 4 = 640V
Power lost would be 640 x 160 = 102 400 W, just 2.6% of the 4MW being sent.

Therefore, increasing the voltage reduces p.d. across cable, reducing power lost.

 

[eureka!]

Left

Thumb thrust/motion/movement
First finger field
Second finger (conventional) current.
Twist your hand to get two of the three turned the right way and you'll figure out the third.

 

[gary221]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s10_qp_31.pdf
part (b) Q 11

Okay, we know that Resistance α length/Area.
Since the coil has a diameter half of that the original one → area of the new coil = ¼ Area of the original one.
Which means, keeping length constant, the new resistance should have been R = length/(Area/4) → R = 4length/Area → R = 4(Resistance of original coil) = 4*4 = 16 ohm.

Whereas, the new resistance is actually V/I → 1.8/0.3 = 6 ohm.
Since R α L → ratio of resistances = ratio of lengths → 6/16 * 100 = 37.5%

Hope you get it.

 

[hard_worker]

Okay, we know that Resistance α length/Area.
Since the coil has a diameter half of that the original one → area of the new coil = ¼ Area of the original one.
Which means, keeping length constant, the new resistance should have been R = length/(Area/4) → R = 4length/Area → R = 4(Resistance of original coil) = 4*4 = 16 ohm.

Whereas, the new resistance is actually V/I → 1.8/0.3 = 6 ohm.
Since R α L → ratio of resistances = ratio of lengths → 6/16 * 100 = 37.5%

Hope you get it.

THANK YOU

 

[rida.12.!!]

this question

 

[rida.12.!!]

diagram of a dc motor

 

[gary221]

this question
View attachment 43117

http://www.s-cool.co.uk/a-level/phy...therford-alpha-particle-scattering-experiment

 

[gary221]

diagram of a dc motor

http://gaullyblog.files.wordpress.com/2011/11/dcmotor.gif

 

[rida.12.!!]

http://www.s-cool.co.uk/a-level/phy...therford-alpha-particle-scattering-experiment

thx

 

[rida.12.!!]

http://gaullyblog.files.wordpress.com/2011/11/dcmotor.gif

thx a lot

 

[AYK998]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w13_qp_31.pdf
question 10b1 pleaseee

 

[hard_worker]

this question
View attachment 43117

well this is smthin u shud know by heart now! go through the notes again for sure ur finding the ans

 

[AYK998]

smone help winter 13
plzzz

 

[princess sofia]

(ii) The gardener is told that, by painting the drum white, he can reduce the quantity of
radiation absorbed and so reduce the rate of evaporation.
Describe an experiment to show that black surfaces are better absorbers of
radiation than white surfaces. You may include a diagram.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
............................................................................................................................. [4]
[Total: 6]
cn we use crookes radiometer experiment in thx ? cze its nt mentioned in markscheme