Physics problems

[rz123]

whoever gets time help me out.
explain how a node is formed from two progressive waves.

two parallel plates P and Q are separated by a distance of 7.6mm in a vacuum. there is a potential difference of 250V between the plates. electrons are produced at X (which is showing direction from plate p to q), these electrons accelerate from rest and travel to plate Q. the electric field between plates may be assumed to be uniform.
a DETERMINE THE FORCE on an electron due to the electric field.
b show that the change in kinetic energy of an electron as it moves from plate P to Q is 4.0 X 10^-17 J
c determine the speed of an electron as it reaches plate Q.
D the positions of the plates are adjusted so that the electric field between them is not uniform. the potential difrnc remains unchanged.
state and explain the effect, if any, of the adjustment on the speed of an electron as it reaches plate Q.

 

[CaptainDanger]

I would have but doing O level....

 

[libra94]

stationary waves are formed when 2 progressive waves of same wavelength and amplitude travelling in opp. directions superimpose.....the point where 2 waves meet is the node, where there is no displacement

 

[libra94]

electric feild (E)= V/d and also E=F/q
where V is the p.d., d is the distance bw 2 plates, F is the force on the charge and q is the charge.

so first u find E=V/d (make sure ur d is in metres!)
so E= 250/ (7.6/1000)
E= 32900 V/m

then E= F/q
F=E q
*chrge of an electron is 1.6*10^-19 C
32900 * 1.6*10^-19
=5.3 * 10 ^-15 N

 

[libra94]

b) change in K.E is equal to work done = force * distance
u know the force, and u know the distance btween 2 plates, then u can calculate ur change in KE

 

[libra94]

K.E= 1/2 m v ^2
u hav the k.e and the mass (the mass is given on the first page of the paper...9.11*10^-31 kg

 

[rz123]

no problem captain danger sahab, and as usual thanks a million libra94

 

[rz123]

the battery in the circuit has an emf of 5.4 V and drives a current of .30 A through the lamp. voltmeter connected parallel to the battery.
the voltmeter reading is 4.8 V . Explain why the voltmeter reading is less than the emf of the battery.

calculate the internal resistance of the battery.

calculate the energy transformed per second in the lamp.

state two assumptions you made in order to complete these calculations.

 

[CaptainDanger]

 

[ManishAdhikari]

u have got answers for others I guess. There is no change is speed of electron because although the field is non uniform it gains same energy and hence the same speed for acceleration