In order for convection to transfer heat, particles need to
2 answers:
You might be interested in
Answer:
A typical example of where the continuity equation can be applied, is in finding the cross sectional area of a laminar falling stream of water from a pipe at an elevation, at the point where it hits the ground.
The speed of the water through the discharge opening of the pipe can be measured with a flow-meter, and the cross sectional opening of the pipe is known.
As the water leaves the pipe, and falls towards the ground, the water stream is accelerated under gravity, and the speed of the water stream increase. The increase in the speed of the water stream causes the cross sectional area to decrease in obedience of the continuity law and equation. If the speed of can be measured, then the area of the water stream just before the water touches the ground can be calculated from the continuity equation.
If the speed of the water stream can not be measured, then it can be calculated using Newton' equation of motion
where
v = the velocity of the water stream at the point where it hits the ground
u = the velocity of the water at the pipe discharge (measured with a flow meter in the pipe)
g = acceleration due to gravity
z = the elevation of the pipe above the ground.
After calculating the speed of the water stream at the point where it hits the ground, the cross sectional area of the the stream can be calculated from the continuity equation.
where
u and v are the velocities of the water stream at the pipe discharge and at the ground respectively.
A = the cross sectional area of the pipe
a = the area of the water stream before it hits the ground.
the equation is simplified as
Answer:
a) - the resistance is proportional to the length of the metal
- a thicker rod, since resistance decreases with increasing area
b) The current is proportional to the area so this is the factor that is influenced by the electric field
Explanation:
a) When the rod is connected to the rod an electrical circuit described by the expression is formed
V = I R
I = V / R
The resistance of the rod is
R = ρ L / A
Where ρ is the resistivity of metal, L Longitud and A cross section.
If a higher current is measured when the other rod is connected, it implies that the resistance has decreased. To have a decrease in resistance you have two possibilities
- use a shorter rod, since the resistance is proportional to the length of the metal
- Use a thicker rod, since resistance decreases with increasing area, remember that the area of a circle is
A = π R²
Therefore, small increases in the diameter of the rod could give great changes in resistance.
b) The current is defined with the charge that crosses a surface per unit of time, when the electric field increases the electrons feel a greater force, therefore the current increases.
The charge number on a wire is
Q = q n Δt A
So up to date is
I = q n When the rod is connected to the rod an electrical circuit described by the expression is formed
V = I R
I = V / R
The resistance of the rod is
R = rho L / A
Where rho is the resistivity of metal, L e; Long and A cross section.
If a higher current is measured when the other rod is connected, it implies that the resistance has decreased. To have a decrease in resistance you have two possibilities
.- use a shorter rod, since the resistance is proportional to the length of the metal
. - Use a thicker rod, since resistance decreases with increasing area, remember that the area of a circle is
A = pi R2
Therefore, small increases in the diameter of the rod could give great changes in resistance.
.b) The current is defined with the charge that crosses a surface per unit of time, when the electric field increases the electrons feel a greater force, therefore the current increases.
The load number on a wire is
Q = q n Dt A
So current is
I = q n v_{d} A
The drag speed (v_{d}) is constant in the materials, it depends on the purity and imperfections, so a change in the length does not significantly change the current.
The current is proportional to the area so this is the factor that is influenced by the electric field
The drag speed (vd) is constant in the materials, it depends on the purity and imperfections, so a change in the length does not significantly change the current.
The current is proportional to the area so this is the factor that is influenced by the electric field