Calculus 3 : Divergence Theorem

Study concepts, example questions & explanations for Calculus 3

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Example Questions

Example Question #1 : Divergence Theorem

Find the divergence of the function \(\displaystyle F(x,y)=(3x+5y)\widehat{i}+5xy^2\widehat{j}\) at \(\displaystyle (-1,2)\)

Possible Answers:

\(\displaystyle -17\)

\(\displaystyle -22\)

\(\displaystyle -52\)

\(\displaystyle 12\)

\(\displaystyle 23\)

Correct answer:

\(\displaystyle -17\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y)=(3x+5y)\widehat{i}+5xy^2\widehat{j}\) at \(\displaystyle (-1,2)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y)\)

Then sum the results together:

\(\displaystyle divF(x,y)=(3)+(10xy)\rightarrow -17\)

Example Question #81 : Surface Integrals

Find the divergence of the function \(\displaystyle F(x,y)=5y^2\widehat{i}+3x\widehat{j}\) at \(\displaystyle (3,4)\)

Possible Answers:

\(\displaystyle 43\)

\(\displaystyle 52\)

\(\displaystyle 33\)

\(\displaystyle 0\)

\(\displaystyle 89\)

Correct answer:

\(\displaystyle 0\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y)=5y^2\widehat{i}+3x\widehat{j}\) at \(\displaystyle (3,4)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y)\)

Then sum the results together:

\(\displaystyle divF(x,y)=(0)+(0)\rightarrow 0\)

Example Question #82 : Surface Integrals

Find the divergence of the function \(\displaystyle F(x,y)=2x^3y^2\widehat{i}+x^2\widehat{j}\) at \(\displaystyle (1,3)\)

Possible Answers:

\(\displaystyle 55\)

\(\displaystyle 63\)

\(\displaystyle 27\)

\(\displaystyle 54\)

\(\displaystyle 33\)

Correct answer:

\(\displaystyle 54\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y)=2x^3y^2\widehat{i}+x^2\widehat{j}\) at \(\displaystyle (1,3)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y)\)

Then sum the results together:

\(\displaystyle divF(x,y)=(6x^2y^2)+(0)\rightarrow 54\)

Example Question #1 : Divergence Theorem

Find the divergence of the function \(\displaystyle F(x,y)=3xy\widehat{i}+2y\widehat{j}\) at \(\displaystyle (2,4)\)

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 18\)

\(\displaystyle 14\)

\(\displaystyle 9\)

\(\displaystyle 13\)

Correct answer:

\(\displaystyle 14\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y)=3xy\widehat{i}+2y\widehat{j}\) at \(\displaystyle (2,4)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y)\)

Then sum the results together:

\(\displaystyle divF(x,y)=(3y)+(2)\rightarrow 14\)

Example Question #2 : Divergence Theorem

Find the divergence of the function \(\displaystyle F(x,y)=(x^2+xy)\widehat{i}+3x^3\widehat{j}\) at \(\displaystyle (-2,5)\)

Possible Answers:

\(\displaystyle 37\)

\(\displaystyle -6\)

\(\displaystyle -30\)

\(\displaystyle 1\)

\(\displaystyle -9\)

Correct answer:

\(\displaystyle 1\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y)=(x^2+xy)\widehat{i}+3x^3\widehat{j}\) at \(\displaystyle (-2,5)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y)\)

Then sum the results together:

\(\displaystyle divF(x,y)=(2x+y)+(0)\rightarrow1\)

Example Question #83 : Surface Integrals

Find the divergence of the function \(\displaystyle F(x,y)=(3x+3y)\widehat{i}+(2x+2y)\widehat{j}\) at \(\displaystyle (2,3)\)

Possible Answers:

\(\displaystyle 18\)

\(\displaystyle 12\)

\(\displaystyle 5\)

\(\displaystyle 0\)

\(\displaystyle 25\)

Correct answer:

\(\displaystyle 5\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y)=(3x+3y)\widehat{i}+(2x+2y)\widehat{j}\) at \(\displaystyle (2,3)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y)\)

Then sum the results together:

\(\displaystyle divF(x,y)=(3)+(2)\rightarrow5\)

Example Question #4 : Divergence Theorem

Find the divergence of the function \(\displaystyle F(x,y,z)=3xy^3\widehat{i}+4xz\widehat{j}+5x^3y\widehat{k}\) at \(\displaystyle (3,2,5)\)

Possible Answers:

\(\displaystyle 129\)

\(\displaystyle 24\)

\(\displaystyle 72\)

\(\displaystyle 167\)

\(\displaystyle 77\)

Correct answer:

\(\displaystyle 24\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y,z)=3xy^3\widehat{i}+4xz\widehat{j}+5x^3y\widehat{k}\) at \(\displaystyle (3,2,5)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y,\widehat{k}:z)\)

Then sum the results together:

\(\displaystyle divF(x,y,z)=(3y^3)+(0)+(0)\rightarrow24\)

Example Question #1 : Divergence Theorem

Find the divergence of the function \(\displaystyle F(x,y,z)=4yz^2\widehat{i}+2xyz\widehat{j}+3xz\widehat{k}\) at \(\displaystyle (-2,0,4)\)

Possible Answers:

\(\displaystyle 14\)

\(\displaystyle 0\)

\(\displaystyle -22\)

\(\displaystyle -19\)

\(\displaystyle -6\)

Correct answer:

\(\displaystyle -22\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y,z)=4yz^2\widehat{i}+2xyz\widehat{j}+3xz\widehat{k}\) at \(\displaystyle (-2,0,4)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y,\widehat{k}:z)\)

Then sum the results together:

\(\displaystyle divF(x,y,z)=(0)+(2xz)+(3x)\rightarrow-22\)

Example Question #1 : Divergence Theorem

Find the divergence of the function \(\displaystyle F(x,y,z)=2xz^2\widehat{i}+xy\widehat{j}-z^3\widehat{k}\) at \(\displaystyle (4,1,-1)\)

Possible Answers:

\(\displaystyle 8\)

\(\displaystyle -1\)

\(\displaystyle -5\)

\(\displaystyle 9\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 9\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y,z)=2xz^2\widehat{i}+xy\widehat{j}-z^3\widehat{k}\) at \(\displaystyle (4,1,-1)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y,\widehat{k}:z)\)

Then sum the results together:

\(\displaystyle divF(x,y,z)=(2z^2)+(x)+(3z^2)\rightarrow9\)

Example Question #2 : Divergence Theorem

Find the divergence of the function \(\displaystyle F(x,y,z)=9xyz\widehat{i}-x^2z^2\widehat{j}+3xyz\widehat{k}\) at \(\displaystyle (0,1,2)\)

Possible Answers:

\(\displaystyle 15\)

\(\displaystyle 7\)

\(\displaystyle 18\)

\(\displaystyle 21\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 18\)

Explanation:

Divergence can be viewed as a measure of the magnitude of a vector field's source or sink at a given point.

To visualize this, picture an open drain in a tub full of water; this drain may represent a 'sink,' and all of the velocities at each specific point in the tub represent the vector field. Close to the drain, the velocity will be greater than a spot farther away from the drain.

Vectorfield

What divergence can calculate is what this velocity is at a given point. Again, the magnitude of the vector field.

We're given the function

\(\displaystyle F(x,y,z)=9xyz\widehat{i}-x^2z^2\widehat{j}+3xyz\widehat{k}\) at \(\displaystyle (0,1,2)\)

What we will do is take the derivative of each vector element with respect to its variable \(\displaystyle (\widehat{i}:x,\widehat{j}:y,\widehat{k}:z)\)

Then sum the results together:

\(\displaystyle divF(x,y,z)=(9yz)+(0)+(3xy)\rightarrow18\)

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