diff --git a/_psets/10.md b/_psets/10.md index 3c5f4ec434453ceff424119c9a13b9b3efc66da7..60dcbff600083ce68578df77fc960de6acc47d3f 100644 --- a/_psets/10.md +++ b/_psets/10.md @@ -179,10 +179,10 @@ coercivity of iron is $$\num{4e3} \si{A/m}$$. Approximately what current would be required in a straight wire to be able to erase a $$\gamma \text{-} Fe_2 O_3$$ recording at a distance of 1 cm? -As found in problem 6.4 in [problem set 4](/psets/04.html), the magnitude of the magnetic field a -distance $$r$$ away from an infinitely long and thin conductor carrying a current $$I$$ is $$I/(2 -\pi r)$$. To erase information stored on $$Fe_2 O_3$$ we need this field to be about as strong as -the coercivity $$H_C = 300 \si{Oe}$$. Thus the current needed is +As found in problem 6.4 in [problem set 4](04.html), the magnitude of the magnetic field a distance +$$r$$ away from an infinitely long and thin conductor carrying a current $$I$$ is $$I/(2 \pi r)$$. +To erase information stored on $$Fe_2 O_3$$ we need this field to be about as strong as the +coercivity $$H_C = 300 \si{Oe}$$. Thus the current needed is $$ \begin{align*} diff --git a/_psets/11.md b/_psets/11.md index f81dbf43d5464d769e7d9457f4714050ab51fa84..53432acac255d3d98ebadf91d37aa91a4dc8fbe8 100644 --- a/_psets/11.md +++ b/_psets/11.md @@ -25,11 +25,11 @@ determine the current, relate the measurement to fundamental constant(s). If a SQUID with an area of $$A = 1 cm^2$$ can detect 1 flux quantum, how far away can it sense the field from a wire carrying 1 A? -As found in problem 6.4 in [problem set 4](/psets/04.html), the magnitude of the magnetic field a -distance $$r$$ away from an infinitely long and thin conductor carrying a current $$I$$ is $$I/(2 -\pi r)$$. One flux quantum is $$\num{2.07e-7} \si{G \cdot cm^2}$$ i.e. $$\num{2.07e-11} \si{T \cdot -cm^2}$$. So to get one flux quantum over $$1 \si{cm^2}$$, we need a magnetic field of -$$\num{2.07e-11} \si{T}$$. Thus a one amp current can be detected at a distance of +As found in problem 6.4 in [problem set 4](04.html), the magnitude of the magnetic field a distance +$$r$$ away from an infinitely long and thin conductor carrying a current $$I$$ is $$I/(2 \pi r)$$. +One flux quantum is $$\num{2.07e-7} \si{G \cdot cm^2}$$ i.e. $$\num{2.07e-11} \si{T \cdot cm^2}$$. +So to get one flux quantum over $$1 \si{cm^2}$$, we need a magnetic field of $$\num{2.07e-11} +\si{T}$$. Thus a one amp current can be detected at a distance of $$ \begin{align*}