Ummmmmmmmmm is this what subject??????? Because I hv no idea unless u tell me a subject
The electric field produced by a large flat plate with uniform charge density on its surface can be found by using Gauss law, and it is equal to

where

is the charge density

is the vacuum permittivity
We see that the intensity of the electric field does not depend on the distance from the plate. Therefore, the strenght of the electric field at 4 cm from the plate is equal to the strength of the electric field at 2 cm from the plate:
Answer: c. 4.56 × 105 J
Explanation:
Given that
mass of lead brick, m= 7.25kg
Temperature T1 = 18.0 °C
Temperature T2 = 328 °C
specific heat capacity of lead, c = 128 J/(kg∙C°)
latent heat of fusion Lfusion =23,200 J/kg
Amount of energy Q =?
Using the formulae
Amount of energy ,Q =mc ( T2-T1)+ mLfusion
7.25kg x 128 J/(kg∙C°) x (328-18°C) + 7.25kg x 23200 J/kg
=455880J
=4.56 x 10^5 J
Answer:
T=7.4 N hence T<30 N
Explanation:
The figure is likely to be similar to the one attached. Writing the equation for forces we have
F-T=Fa/g where F is the force, T is tension, a is acceleration and g is acceleration due to gravity. Substituting the figures we have the first equation as
30 N - T = (30/9.81)a
Also, we know that T=F*a/g and substituting 10N for F we obtain the second equation as
T = (10/9.81)a
Adding the first and second equations we obtain
30 = 4.077471967
a Hence

and T=a hence
T is approximately 7.4 N
Answer:

The rule for kilometers is that every three seconds between a lightning flash and the following thunder gives the distance to the flash in kilometers.
Explanation:
In order to use the rule of thumb to find the speed of sound in meters per second, we need to use some conversion ratios. We know there is 1 mile per every 5 seconds after the lightning is seen. We also know that there are 5280ft in 1 mile and we also know that there are 0.3048m in 1ft. This is enough information to solve this problem. We set our conversion ratios like this:

notice how the ratios were written in such a way that the units got cancelled when calculating them. Notice that in one ratio the miles were on the numerator of the fraction while on the other they were on the denominator, which allows us to cancel them. The same happened with the feet.
The problem asks us to express the answer to one significant figure so the speed of sound rounds to 300m/s.
For the second part of the problem we need to use conversions again. This time we will write our ratios backwards and take into account that there are 1000m to 1 km, so we get:

This means that for every 3.11s there will be a distance of 1km from the place where the lightning stroke. Since this is a rule of thumb, we round to the nearest integer for the calculations to be made easily, so the rule goes like this:
The rule for kilometers is that every three seconds between a lightning flash and the following thunder gives the distance to the flash in kilometers.