If the small (induced) coil is positioned 45 o to the Helmholtz Coils, the induced emf will decrease. The reason behind this is that Φ=BAcos (𝛳), which is involved in the calculations of emf. If ever that the angle turn into 45 o the value of Φ will get smaller.
Full Answer
sol, the cross-sectional area of the coil, A, and the cosine of the angle between the vector B, and a vector A, normal to the area.
7. As shown by Figure 6, the solenoid’s field is at a maximum near its center and nearly zero far away from the solenoid. Why is the emf produced at both these places so small?
The green triangle to the right of the solenoid indicates the instantaneous direction of the solenoid’s field. The top graph always measures the distance between the center of the solenoid and the tip of the Hall probe or the center of the pickup coil, depending on which one is in use.
2. The solenoid’s field can be measured experimentallyusing a Hall Probe which measures magnetic fields using the Hall Effect. Select the Hall probe from the Sensorlist. The probe measures the magnetic field at its tip so it’s important to place the tip at the center of the solenoid in this part of the lab. Either the solenoid or the probe can be dragged horizontally to adjust this alignment. We want to keep the solenoid in one location so if you’ve moved it, drag it to where its left end is at about the 0 cm point and leave it in place. (This is the default location.) Then drag the probe until its tip is near the center of the solenoid. (The solenoid is magically somewhat transparent.) 3. Click the Start Databutton. (In the future this instruction will be abbreviated to simply Start Data. ) 4. Three graphs are produced. The top one records the separation distance between the center of the solenoid and the tip of the probe when the probe is in use. This graph should be a horizontal line nearly or exactly coincident with the horizontal axis. If they’re coincident, you have the probe aligned just where it needs to be. That’s a tough call. But try this. Click on the Graph Tool, the vertical line that crosses all three graphs. Note the readings to the right of the Graph Tool You should see something like “Separation = 0.020 m.” This is a more precise reading of the value that you want to be equal to zero. Always use this tool for alignment. Here’s how. Drag the Graph Tool over near the left end of the graph. Start Data. The graph trace will now quickly arrive at the Graph Tool. If it reads a separation of more than 2 mm, adjust the probe’s location a bit and retry. 5. Once you have a good run with a small separation, have a look at the middle graph. It records the voltage drop across the 5.00 Ω resistor in series with the power supply and solenoid. A wire from each side of the resistor connects to the computer interface which measures this voltage drop. (This parallel connection diverts a negligible current due to its large resistance.) From the horizontal blue line and the scale of the graph you should read a constant potential difference of about 30.00 volts. Since the resistor has a value of 5.00 Ω, the resistor current would be the voltage drop divided by 5.00 Ω. Thus it should be about 6.00 A. This is the current through the solenoid which is in series with the resistor. 6. The Graph Tool provides a more precise reading of the voltage drop across the solenoid and the current through it. So we’ll always use it for taking data. Drag this tool from side to side. Since the voltage drop and current are both constant, the only change you see is the time reading. So the graph is plotted over time and the graph tool allows you to easily read current and voltage drop at the time of your choosing. As you’ll soon see, our currents and voltages won’t stay constant for long. 7. The bottom graph displays the magnetic field measured by the probe at its tip. This should be constant in this case. Record this value below in both Gauss and Tesla units. Remember 1 Gauss = 10-4Tesla. You’ll use Teslas in your calculations elsewhere in this lab. Round the experimental values to the nearest Gauss.
Clearly the magnetic field is strongest at the center of the solenoid and drops off as you move away from the center. We’ll take advantage of this relatively constant Bduring the rest of this lab by working near the center of our solenoid.
The Hall probe is a transducer that measures the strength of a magnetic field. We’ll now look at another device that reacts in a different way to a magnetic field. A coil of wire doesn’t respond to a magnet field but rather to a change in magnetic flux