Physics : asked on dwhitlock10
 04.06.2020

The first charge is pulling on the second. Is the second pulling on the first? Explain your reasoning

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24.06.2023, solved by verified expert
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law of action and reaction.

Explanation:

In Newton's three laws it is established that forces act in pairs, if one body interacts with another the second interacts with the first, this is the so-called law of action and reaction.

In this case, when the first load pulls on the second, the second pulls on the first, the two forces are not canceled because each one is applied to a different body.

Therefore the magnitude of the forces is the same, but the direction is opposite and each one is applied in a body

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Physics
Step-by-step answer
P Answered by PhD

(a) 3.33

For a capacitor with dielectric disconnected from the battery, the relationship between the voltage across the capacitor without the dielectric (V) and with the dielectric (V) is given by

V' = \frac{V}{k}

where

k is the dielectric constant of the material

In this problem, we have

V' = 3.6 V

V=12 V

So we can re-arrange the formula to find the dielectric constant:

k=\frac{V}{V'}=\frac{12 V}{3.6 V}=3.33

(b) The energy stored reduces by a factor 3.33

The energy stored in a capacitor is

U=\frac{1}{2}QV

where

Q is the charge stored on the capacitor

V is the voltage across the capacitor

Here we can write the initial energy stored in the capacitor (without dielectric) as

U=\frac{1}{2}QV

while after inserting the dielectric is

U'=\frac{1}{2}QV' = \frac{1}{2}Q\frac{V}{k}

since Q, the charge, has not changed (the capacitor is disconnected, so the charge cannot flow away from the capacitor).

So the ratio between the two energies is

\frac{U'}{U}=\frac{\frac{1}{2}Q\frac{V}{k}}{\frac{1}{2}QV}=\frac{1}{k}

which means

U' = \frac{U}{k}=\frac{U}{3.33}

So, the energy stored has decreased by a factor 3.33.

(c) 5.5 V

Pulling the dielectric only partway so that it fills half of the space between the plates is equivalent to a system of 2 capacitors in parallel, each of them with area A/2 (where A is the original area of the plates of the capacitor), of which one of the two is filled with dielectric while the other one is not.

Calling

C=\frac{\epsilon_0 A}{d} the initial capacitance of the capacitor without dielectric

The capacitance of the part of the capacitor of area A/2 without dielectric is

C_1 = \frac{\epsilon_0 \frac{A}{2}}{d}= \frac{C}{2}

while the capacitance of the part of the capacitor with dielectric is

C_2 = \frac{k \epsilon_0 \frac{A}{2}}{d}= \frac{kC}{2}

The two are in parallel, so their total capacitance is

C' = C_1 + C_2 = \frac{C}{2}+\frac{kC}{2}=(1+k)\frac{C}{2}=(1+3.33)\frac{C}{2}=2.17 C

We also have that

V=\frac{Q}{C}=12 V this is the initial voltage

So the final voltage will be

V' = \frac{Q}{C'}=\frac{Q}{2.17 C}=\frac{1}{2.17}V=\frac{12 V}{2.17}=5.5 V

Physics
Step-by-step answer
P Answered by PhD

(a) 3.33

For a capacitor with dielectric disconnected from the battery, the relationship between the voltage across the capacitor without the dielectric (V) and with the dielectric (V) is given by

V' = \frac{V}{k}

where

k is the dielectric constant of the material

In this problem, we have

V' = 3.6 V

V=12 V

So we can re-arrange the formula to find the dielectric constant:

k=\frac{V}{V'}=\frac{12 V}{3.6 V}=3.33

(b) The energy stored reduces by a factor 3.33

The energy stored in a capacitor is

U=\frac{1}{2}QV

where

Q is the charge stored on the capacitor

V is the voltage across the capacitor

Here we can write the initial energy stored in the capacitor (without dielectric) as

U=\frac{1}{2}QV

while after inserting the dielectric is

U'=\frac{1}{2}QV' = \frac{1}{2}Q\frac{V}{k}

since Q, the charge, has not changed (the capacitor is disconnected, so the charge cannot flow away from the capacitor).

So the ratio between the two energies is

\frac{U'}{U}=\frac{\frac{1}{2}Q\frac{V}{k}}{\frac{1}{2}QV}=\frac{1}{k}

which means

U' = \frac{U}{k}=\frac{U}{3.33}

So, the energy stored has decreased by a factor 3.33.

(c) 5.5 V

Pulling the dielectric only partway so that it fills half of the space between the plates is equivalent to a system of 2 capacitors in parallel, each of them with area A/2 (where A is the original area of the plates of the capacitor), of which one of the two is filled with dielectric while the other one is not.

Calling

C=\frac{\epsilon_0 A}{d} the initial capacitance of the capacitor without dielectric

The capacitance of the part of the capacitor of area A/2 without dielectric is

C_1 = \frac{\epsilon_0 \frac{A}{2}}{d}= \frac{C}{2}

while the capacitance of the part of the capacitor with dielectric is

C_2 = \frac{k \epsilon_0 \frac{A}{2}}{d}= \frac{kC}{2}

The two are in parallel, so their total capacitance is

C' = C_1 + C_2 = \frac{C}{2}+\frac{kC}{2}=(1+k)\frac{C}{2}=(1+3.33)\frac{C}{2}=2.17 C

We also have that

V=\frac{Q}{C}=12 V this is the initial voltage

So the final voltage will be

V' = \frac{Q}{C'}=\frac{Q}{2.17 C}=\frac{1}{2.17}V=\frac{12 V}{2.17}=5.5 V

Physics
Step-by-step answer
P Answered by PhD

0.0048 N

Explanation:

The electric force acting on a particle is given by

F=qE

where

q is the charge

E is the magnitude of the electric force

F is the strength of the force

The force has the same direction as the field if the charge is positive, and the opposite direction if the charge is negative.

In this problem, we have:

Q=4.0\cdot 10^{-9}C is the charge

E=1.2\cdot 10^6 N/C is the electric field

Therefore, the electric force on the charge is

F=QE=(4.0\cdot 10^{-9})(1.2\cdot 10^6)=0.0048 N

Physics
Step-by-step answer
P Answered by PhD

0.0048 N

Explanation:

The electric force acting on a particle is given by

F=qE

where

q is the charge

E is the magnitude of the electric force

F is the strength of the force

The force has the same direction as the field if the charge is positive, and the opposite direction if the charge is negative.

In this problem, we have:

Q=4.0\cdot 10^{-9}C is the charge

E=1.2\cdot 10^6 N/C is the electric field

Therefore, the electric force on the charge is

F=QE=(4.0\cdot 10^{-9})(1.2\cdot 10^6)=0.0048 N

Physics
Step-by-step answer
P Answered by PhD

4.8 × 10^15 N

Explanation:

Electric Field is defined as Force per unit Charge.

This is expressed mathematically as;

E= F/Q

Where E- Electric Field

F- Force

Q- charge

From the expression above by change of subject of formula for F, we have;

F=E×Q

= 1.2 * 10^6 ×4.0 * 10^9

= 4.8 × 10^15 N

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