physics!!!!!!!!!!!!!!!!!!!!!!!

[halosh92]

ELECTRICITY:



1)which of the following describes the electric potential difference between two points in a wire that carries a current?
a) the force required to move a unit positive charge between the ponts
b) the ratio of the energy dissipated between the points to  the current
c) the ratio of the power dissipated between the points to the current
d) the ratio of power disipated between the points to the charge moved.

wats the answer and why is it so?

2) two parallel metal plates P and Q are situated 8.0cm apart in air
plate Q is earthed and plate P is maintained at a potential of +160V
a) on a figure draw lines to represent the electric field in the region between the plates


what do they mean by earthed? and wats the direction of the field lines???

[astarmathsandphysics]

P=vi so v=p/i answer is b will answer the other when I get home

[halosh92]

ELECTRICITY:



1)which of the following describes the electric potential difference between two points in a wire that carries a current?
a) the force required to move a unit positive charge between the ponts
b) the ratio of the energy dissipated between the points to  the current
c) the ratio of the power dissipated between the points to the current
d) the ratio of power disipated between the points to the charge moved.

wats the answer and why is it so?

2) two parallel metal plates P and Q are situated 8.0cm apart in air
plate Q is earthed and plate P is maintained at a potential of +160V
a) on a figure draw lines to represent the electric field in the region between the plates


what do they mean by earthed? and wats the direction of the field lines???

the magnitude of the  electric field between the plates is 2.0 * 10 ^3 V/m

b) a dust partcle is suspended in the air between the plates. the particle has charges of ( + 1.2 * 10^-15 C)  and (-1.2 * 10^-15 C) near its ends. the charges may be considered to be point charges separated by a distance of 2.5mm.
the particle makes an angle of 35 degrees, with the direction of the electric field.
i) on a figure draw arriws to show the direction of the force on each charge due to the electric field.
ii) calculate the magnitude of the force on each charge due to the electric field
iii)  determine the magnitude of the couple acting on the particle
iv) suggest the subsequent motion of the particle in the electric field

[halosh92]

3) two horizontal metal plates X and Y are at a distance 0.75cm apart. a positively charged particle of mass (9.6 * 10^-15) kg
is situated in a vacuum between the plates.
the potential difference between the plates is adjusted until the particles remains stationary.
a) state a reason, which plate X or Y , is positively charged
b)the potential difference required for the particle to be stationary between the plates is found to be 630 V. calculate.
i) the electric field strength between the plates
ii) the charge on the particle



4) an electron travelling horizontally in a vacuum enters the region between two horizontal metal plates.
the lower plate is earthed and the upper plate is at a potential of +400V. the separation of the plates is 0.80cm
the electric field between the plates may be assumed to be uniform and outside the plates to be zero
ai) Draw an arrow on the electron to show the direction of the force on the electron due to the electric field between the plates
ii) sketch the path of the electron as it passes between the plates and beyond them.
b) determine the electric field strength E between the plates.
cI) calculate, for the electron between the plates, the magnitude of :
i) the force on the electron
ii) its acceleration
d) state and explain the effect , if any of this electric  field on the horizontal component of the motion of the electron.

[vanibharutham]

I have not done fields yet, but i reckon i can try and explain question 1 on electricity

Its useful to learn the definitions:

ELECTROMOTIVE FORCE, is the energy transferred per unit charge from a cell to the circuit... i.e. amount of energy that is converted to electrical energy per unit charge.

POTENTIAL DIFFERENCE, is the energy transferred per unit charge from the circuit to a component and converted to other forms.... i.e. the amount of electrical energy converted to other forms of energy per unit charge

Therefore,

from the definitions above:

Potential Difference = E/Q (e = energy, q = charge)
Learn the things above, they are useful for electricity


P = IV

Therefore,

V = P / I

therefore potential difference is a ratio of power dissipated to the current

[nid404]

4)

i) arrow on electron pointing towards positive plate
ii) electron leaves closer to the positive end.

b) E=V/d
V=400V
d=0.8X10^-2m

E=50000 V/m

c) i) F=EQ
Q=charge on eletcron
F=50000X1.6X10^(-19)
=8X10^(-15)

ii) F=ma
m of electron=9.1X10^(-31) kg
8X10^(-15)=9.11X10^(-31) X a
a=8.8X10^15

d)No effect since force of gravity is normal to horizontal motion

[halosh92]

4)

i) arrow on electron pointing towards positive plate
ii) electron leaves closer to the positive end.

b) E=V/d
V=400V
d=0.8X10^-2m

E=50000 V/m

c) i) F=EQ
Q=charge on eletcron
F=50000X1.6X10^(-19)
=8X10^(-15)

ii) F=ma
m of electron=9.1X10^(-31) kg
8X10^(-15)=9.11X10^(-31) X a
a=8.8X10^15

d)No effect since force of gravity is normal to horizontal motion

which plate is negative and which is positive? and why is the force towards the postive???
and is the mass of electron always 9.1X10^(-31) kg
thxx alott
By the way thx vani 

[nid404]

I haven't seen the diagram mate :/
The side to which the positive terminal is connected is always positive....
The force on the electron is towards the positive.....becuz electron is negatively charged.
but if they're asking for the* electric field*, it's from positive to negative.

Yes mass of electron is constant....it's mentioned in the data booklet

[halosh92]

a copper wire of cross sectional area 2.0mm^2 carries a current of 10A
how many electrons pass through a given cross section of the wire in one second?

[nid404]

Q=IT
Q=10C
charge on one electron 1.6X10^-19 C
no of electrons in 10C=10/  1.6X10^-19 C
                               =6.25X10^19

[halosh92]

when a potential difference V is applied between the ends of a wire of diameter "d" and length "l", the current in the wire is 'I"
what is the current when a potential difference of 2V is applied between the ends of a wire of the same
material of diameter 2d and the length "2l" ? assume that the temperature of the wire remains constant?
a) I
b) 2I
c) 4I
d) 8I

[vanibharutham]

Using the idea of Resistivity (NOT RESISTANCE)

The following will stay constant between the two different wires:

1) Resistivity, p, which is an intrinsic property of the materials and is a measure of the resistance of 1m³ of a substance.

Anyways:

R = p L / A
( R = resistance, p = resistivity, L = length, A = cross sectional area)

For first wire:

R = 4 p L / pi d²

V = I R

I = V pi d² / 4 p L


For second wire:

R = 2 p L / pi d²

x I = 2V pi d² / p L

x = 8

Therefore d)

[halosh92]

thankyou

two wires made of the same material and of the same length are connected in  parallel to the same voltage supply  wire P has a diameter of 2mm. wire Q has a diameter of 1mm
whats is the ratio current in P/current  in Q
a) 1/4
b) 1/2
c) 2
d) 4

[astarmathsandphysics]

a cos R pl/A=pl/pi(d/2)2 so if d is double the current is halved

[halosh92]

just a few random questions:
 1) a beam, the weight of which maybe neglected , is supported by three identical springs. when a weight W is hung
from the middle of the beam, the extensionj of each spring is X
the middle spring is then removed and the weight is removed .
what is the extension when a weight of 2W is hung from the middle of the beam
a) 3X/2
b) 4X/3
c)2X
c)3X



2) two solid substances P and Q have atoms of masses Mp and Mq respectively.
they have Np and Nq atoms per unit volume
it is found by experiment that the density of P is greater than that of Q
which one is the correct one?
a) Mp>Mq
b)Np>Nq
c)MpNp>MqNq
d)Mp/Np   >    Mq/Nq



3) what is the evidence for the molecules in solids and liquids having approximately the same separation??




4) a hard ball and a soft ball with equal masses and volumes are thrown at a glass window the ball hits the window at the same speed . suggest why the hard ball is more likely than the soft ball break the window?


thx alottttt