11. As shown in figure 11-1-6, the electromotive force of the power supply is 3V, the internal resistance is ignored, the mass of the conductor rod is 60g, the length is 1m, the resistance is 1.5 Ω, the direction of the uniform magnetic field is vertical upward, and the size is 0.4t. When the switch s is closed, the rod slides from the bottom end of the fixed smooth insulating ring to a certain position and stops (1) What is the pressure of the rod on each ring at this position? (2) If the radius of the insulating ring is known to be 0.5m, what is the height difference between this position and the bottom of the ring? E S B Figure 11-1-6

11. As shown in figure 11-1-6, the electromotive force of the power supply is 3V, the internal resistance is ignored, the mass of the conductor rod is 60g, the length is 1m, the resistance is 1.5 Ω, the direction of the uniform magnetic field is vertical upward, and the size is 0.4t. When the switch s is closed, the rod slides from the bottom end of the fixed smooth insulating ring to a certain position and stops (1) What is the pressure of the rod on each ring at this position? (2) If the radius of the insulating ring is known to be 0.5m, what is the height difference between this position and the bottom of the ring? E S B Figure 11-1-6

What about the picture?

As shown in the figure, the electromotive force of the power supply is 3V, the internal resistance is ignored, the mass of the conductor rod is 60g, the length is 1cm, the resistance is 1.5 ohm, the uniform magnetic field is vertically upward, B = 0.4t
When the switch is closed, the rod slides from the bottom end of the fixed smooth insulating rod to a certain position. How much pressure does the rod exert on each ring at this position? If the radius of the insulating rod is known to be 0.5m, what is the height difference between this position and the bottom of the ring?

(1) 5 N (2) 0.2 m, and then the stress analysis of the conductor bar
E = IR (2)0.2 m
F =BIL
mgsinθ - Fcosθ = 0
So, θ = 37 and 186;
∴F =0.5 N

The resistance wire with a resistance value of 10 ohm is evenly stretched to twice of the original value by wire drawing machine, and the resistance of the conductor becomes?

R = ρ L / s. for each substance, l is the length of the resistance wire and S is the cross-sectional area
If we lengthen the resistance wire by 2 times, the cross-sectional area will be 1 / 2 of the original, ρ will not change, so the resistance will be 4 times of the original, 40 Ω

The resistance wire with a resistance of 1 ohm is evenly elongated to 3 times of the original, and then cut into 3 equal length sections. They are connected in parallel and used as a wire, and the resistance of the wire is increased（
A. Constant B, larger C, smaller D, uncertain

No change
Analysis:
The original resistance is r
After being pulled to three times of the original, according to the volume formula, the cross-sectional area of the conductor must be reduced to one third of the original. That is to say, the three sections of conductor cut out are equal to the original length, and the cross-sectional area becomes one third. According to r = ρ L / s, the resistance of each section of conductor becomes three times of the original (that is 3R)
After three conductors are connected in parallel, the total resistance becomes one third of the original, that is, 1 / 3 * 3R = R