1. The result from direct measurement is more dependable. If we obtain the result from the equation that contains more quantities from measurements, the error will accumulate in the calculation; as the more measurements we have , the more errors occur.
Please see E-2 for detail.

2. The theory of using Wheastone Bridge to measure the resistance of a resistor is to compare the ratio of the unknown resistance to a standard resistance with the ratio of the lenghs of two parts of a uniform conductive wire. The measurement is independent of the fluctuation of the power supply voltage and the built-in resistances of the measuring devices such as voltmeter and ammeter. The result is accurate.
During the experiment, we need to balance the bridge twice, that is, after we first observe the galvanometer's needle pointing to zero, we press the button of the protective circuit, and we can not change resistors while the contact c is depressed, and we never set Rs=0. All these measures are to protect the galvanometer from damage.
See E-3 last part for the reason why we never set Rs=0.

3. Because of the edge effect, the equipotential lines near the two electrodes have greater curvature than those in the middle of the paper. The lines in the middle of the paper are almost straight , the lines near the two extremities, are circular.
As the distance increases, the electric field is getting weaker, hence the potential is smaller; it is difficult to locate the points far away from the electrodes.

4. The measurement of the radius of circular motion of the electrons, r is most uncertain, because of the limitation of the equipment. We are unable to obtain a complete semecircle for the circular orbit of the moving electrons. Our measurement of r is an approximation (r2»x2 + y2).

5. f0 = 1/2pÖLC= 4.5x103Hz
At resonance, Z= R, but this R includes the resistance of the inductor. R = V/Imax = 5V/1.68mA = 2976W
The resistance of the inductor is
2976W - 2.7kW =276W

6. When the emf of the battery is below the specified value, and most important, the internal resistance becomes greater such that it can no longer provide enough electric energy to the external circuit, that is, the current in the circuit is very small.
The relevant equation is
e = v +Ir
where r is the internal resistance of the battery.

7.

The most likely cause is that the fuse for the ammeter is burnt.
The correct way to use ammeter is :

  1. connect the ammeter in series with the circuit elements.
  2. set the correct position for dc, and ac.
  3. The button is at the mA position.
  4. Start measuring current at the highest range(2000mA), then go down step by step until you see three digits.

8. The equation is

RC = (t2 - t1)/(lnV1 - lnV2)
Using semilogarithmic scale for V(voltage measured from the voltmeter) as independent variable versus time, t in linear scale, we draw a straight line whose slope is -RC.

9. See E-10 for detail.

10. From Ip/Is = Vs/Vp, we have
15mA/750mA = Vs/120V
Vs = 2.4V
This is a step-down transfromer.

 
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