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4 years ago

A helium ballon rises to a certain height and then halts. why

Physics

1 answer:

kipiarov [429]4 years ago

3 0

Answer:

Because the density of the atmospheric air becomes equal to the density of the helium.

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Why are animal cells square and animal cells round

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Plant cells are not necessarily square, but they due tend to have distinct edges and be kind of rectangular. This structure is caused by the cell wall which is very rigid and therefore forces the cell to have a more defined shape. However, animal cells do not have a cell wall but only the plasma membrane. Which is is why it's round.

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To reduce friction on an aircraft, the surfaces (skin) are ? and the body is ?

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Surface (skin) should be smooth and body should be streamlined shaped.

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2 years ago

You have a meteorite sample and you decide to use the uranium-235/lead-207 system to date it. After analysis, you find that it h

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3 years ago

A student is experimenting with some insulated copper wire and a power supply. She winds a single layer of the wire on a tube wi

OverLord2011 [107]

Answer:

$P=214.7187\,W$

Explanation:

Given that:

Diameter of the solenoid, $D=10\,cm=0.1\,m$

length of the solenoid, $L=90\,cm=0.9\,m$

diameter of the wire, $d=0.1\,cm=10^{-3}\,m$

magnetic field at the center of the solenoid, $B=7.4\times 10^{-3}\,T$

Now we need the no. of turns incorporated in the length of 90 cm:

$N=\frac{Length\,\,of\,\,solenoid}{diameter\,\,of\,\, wire}$

$N=\frac{L}{d}$

$N=\frac{0.9}{10^{-3}}$

$N=900\,\,turns$

For solenoids we have:

$B=\mu.n.I$ ...............................(1)

where:

$\mu=$ permeability of the medium

n = no. of turns per unit length

I = current in the coil

So,

$n=\frac{900}{0.9}$

$n=1000\,turns\,.\,m^{-1}$

Now putting the respective values in the eq. (1)

$7.4\times 10^{-3}=4\pi\times10^{-7}\times 1000\times I$

$I=5.8887\,A$

For copper we have resistivity:

$\rho=1.72\times 10^{-8}\, \Omega.m$

We know that resistance is given by:

$R=\rho.\frac{l}{a}$ .....................................(2)

where:

l = length of the conducting wire

a = cross sectional area of the conducting wire

Now we need the length (l) of the wire:

Circumference of the solenoid,

$C=\pi.D$

$C=0.1\pi\,m$

$\therefore l=C\times N$

$l=90\pi\,m$

Cross-sectional area of wire:

$a=\pi.\frac{d^2}{4}$

$a=\pi. \frac{(10^{-3})^2}{4}\,m^2$

Resistance from eq. (2):

$R=1.72\times 10^{-8}\times \frac{90\pi}{\pi. \frac{(10^{-3})^2}{4}}$

$R=6.192 \,\Omega$

For power we have:

$P=I^2.R$

$P=5.8887^2 \times 6.192$

$P=214.7187\,W$

6 0

3 years ago

The grid in a triode is kept negatively charged to prevent...

Anestetic [448]

I think the correct answer is the third statement, electron from escaping from the tube containing the triode. The negative charge on the grid repels any electron in the tube. As a result,the flow of current is controlled. If the field is that strong, all current flow will stop resulting to maintaining the electron cloud in the tube.

4 0

3 years ago

Read 2 more answers

A helium ballon rises to a certain height and then halts. why​

A helium ballon rises to a certain height and then halts. why