Question
You measure the magnitude of the external force $\vec{F}$ that must be applied to a rectangular conducting loop to pull it at constant speed $v$ out of a region of uniform magnetic field $\vec{B}$ that is directed out of the plane of Fig. $\mathbf{P 2 9 . 6 6 .}$ The loop has dimensions $14.0 \mathrm{~cm}$ by $8.00 \mathrm{~cm}$ and resistance $4.00 \times 10^{-3} \Omega ;$ it does not change shape as it moves. The measurements you collect are listed in the table.$$\begin{array}{l|lllll}\boldsymbol{F}(\mathbf{N}) & 0.10 & 0.21 & 0.31 & 0.41 & 0.52 \\\hline \boldsymbol{v}(\mathbf{c m} / \mathbf{s}) & 2.0 & 4.0 & 6.0 & 8.0 & 10.0\end{array}$$(a) Plot the data as a graph of $F$ versus $v .$ Explain why the data points plotted this way lie close to a straight line, and determine the slope of the best-fit straight line for the data. (b) Use your graph from part (a) to calculate the magnitude $B$ of the uniform magnetic field. (c) In Fig. $\mathrm{P} 29.66,$ is the current induced in the loop clockwise or counterclockwise? (d) At what rate is electrical energy being dissipated in the loop when the speed of the loop is $5.00 \mathrm{~cm} / \mathrm{s} ?$
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The EMF is also equal to the product of the resistance of the loop and the current flowing through it. Therefore, we can write the force as $F = BIL$, where $B$ is the magnetic field, $I$ is the current, and $L$ is the length of the loop. Show more…
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You measure the magnitude of the external force $\overrightarrow{\boldsymbol{F}}$ that must be applied to a rectangular conducting loop to pull it at constant speed $v$ out of a region of uniform magnetic field $\vec{B}$ that is directed out of the plane of Fig. P29.66. The loop has dimensions $14.0 \mathrm{~cm}$ by $8.00 \mathrm{~cm}$ and resistance $4.00 \times 10^{-3} \Omega ;$ it does not change shape as it moves. The measurements you collect are listed in the table. $$\begin{array}{l|lllll} \boldsymbol{F}(\mathbf{N}) & 0.10 & 0.21 & 0.31 & 0.41 & 0.52 \\ \hline \boldsymbol{v}(\mathrm{cm} / \mathrm{s}) & 2.0 & 4.0 & 6.0 & 8.0 & 10.0 \end{array}$$ (a) Plot the data as a graph of $F$ versus $v$. Explain why the data points plotted this way lie close to a straight line, and determine the slope of the best-fit straight line for the data. (b) Use your graph from part (a) to calculate the magnitude $B$ of the uniform magnetic field. (c) In Fig. $\mathrm{P} 29.66,$ is the current induced in the loop clockwise or counterclockwise? (d) At what rate is electrical energy being dissipated in the loop when the speed of the loop is $5.00 \mathrm{~cm} / \mathrm{s} ?$
You measure the magnitude of the external force $\overrightarrow{F}$ that must be applied to a rectangular conducting loop to pull it at constant speed v out of a region of uniform magnetic field $\overrightarrow{B}$ that is directed out of the plane of $\textbf{Fig. P29.68}$. The loop has dimensions 14.0 cm by 8.00 cm and resistance 4.00 $\times$ 10$^{-3}$ $\Omega$; it does not change shape as it moves. The measurements you collect are listed in the table. (a) Plot the data as a graph of $F$ versus $v$. Explain why the data points plotted this way lie close to a straight line, and determine the slope of the best-fit straight line for the data. (b) Use your graph from part (a) to calculate the magnitude $B$ of the uniform magnetic field. (c) In Fig. P29.68, is the current induced in the loop clockwise or counterclockwise? (d) At what rate is electrical energy being dissipated in the loop when the speed of the loop is 5.00 cm/s?
Calculating the force on a current loop in a magnetic field is more subtle than on a single straight wire. The net force on a current loop in a non-uniform magnetic field is not necessarily zero. In this section, you will calculate the net force on a current circular loop in a diverging magnetic field. Recall that for a bar magnet, the magnetic fields at each end of the magnet are diverging, as illustrated in the sketch. Consider a circular loop of radius R carrying current, with the magnetic field pointing to the right at the loop. At the top of the loop, the top magnetic field vector B is 10 degrees above horizontal, and the bottom magnetic field vector B is 10 degrees below horizontal. The observer on the right sees the current going in the clockwise direction. Sketch the force vector at the top and bottom of the circular loop. What is the magnitude of the horizontal component of the force on a small length of wire ds at the top of the loop? (Note that the vertical components of force should have canceled with each other in your sketch.) Integrate over the length of the loop to find the net force on the loop. Does the force increase or decrease as the coil is moved to the right? Explain your response.
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