What should we pay attention to when measuring resistance and current with Multimeter

What should we pay attention to when measuring resistance and current with Multimeter

Pay attention to the position and gear of the meter

A physics experiment about "measuring resistance with multi-purpose meter",
A: Put the selection switch in "X1" position; B: insert the probe into the socket, first contact the two pens, and rotate the zero adjustment knob to make the pointer point to the zero position of the resistance scale; C: connect the two probes to the two ends of a resistance to be measured, and it is found that the pointer deflection is small; D: change the "X100" position, and it is found that the pointer deflection is moderate, Then write down the resistance value; E: after pulling the meter out of the socket, put the multi-purpose meter back on the desk, and the experiment is over
Q: which steps did the student violate the rules in the experiment?

switches to X100 files, it needs to take two short cuts and then zero.
Also, after use, turn the multimeter to the off position

What's the difference between using a multimeter to measure resistance, using a voltmeter and an ammeter to measure resistance and using a bridge to measure resistance?
It is a thinking problem of DC resistance test experiment

The measurement of resistance by electric bridge will not cause error because of the internal resistance of the meter. The selection of measuring range is based on the formula r = u / I, the change of resistance Δ R, and the change of current Δ I. according to the image of resistance with current and hyperbolic image, it can be seen that when the current is large, the change of current and the corresponding change of resistance is very small, so it is not accurate

What is the minimum value of current and the maximum power consumption in the circuit composed of two resistances of 3 Ω and 6 Ω and a power supply of 3V?

When the current is minimum, that is, when the total resistance of the circuit is maximum
When two resistors are connected in series, the resistance is the largest, r = 3 + 6 = 9 ohm
Imain = u / R total = 3 / 9 = 0.33a
As for the maximum power consumption of the whole circuit, P total = u total x u total / R total is the best
Because for the whole circuit, u will never change, always the power supply voltage
Therefore, if P is always the largest, only R is always the smallest
For the two resistors, the total resistance is the smallest and can only be paralleled. After paralleling, the total resistance R is total = 3x6 / (3 + 6) = 2 ohm
Ptotal = 3x3 / 2 = 4.5w