Question

1. What is the difference between “resistance” and “resistivity”?

2. What is the rated resistance of a resistor coded with the color bands: Brown-Gray-White? (Google resistor color codes)

3. Voltmeters measure electric potential; ammeters measure electric current. Which of these two types of measuring device is likely to have an extremely high internal resistance? Which is likely to have a very low internal resistance? Explain your answers.

4. Suppose you have two light bulbs, A and B, which are identical in their construction except that the wire filament in bulb B is twice as thick as the wire filament in bulb A. If you apply the same voltage to the two bulbs, which glows brighter? Assuming the same operating efficiency for the two bulbs, how much brighter?

Answer 1

1. Resistance is the opposition offered by a conductor to the current flowing through it. It depends on the physical condition of conductor like length, cross sectional area temperature etc. When the physical condition of a conductor is changes it's resistance also changes. Unit of resistance is "ohm" or .
If a p.d. applied across a conductor is V and current flowing through it is I the resistance of conductor R is given by
R = V/I

While resistivity is the property of a material, it does not depends on physical condition of material.
Resistivity of a material is the resistance offered by a conductor of unit length and unit cross-sectional area made by that material. It's unit is ohm m or m
If a conductor of length L, cross-sectional area A has resistance R then its resistivity can be given as

2. Brown-Gray-White

Here Brown indicates 1 Gray indicates 8 and White indicates 9
Now resistance can be calculated by

Colour, Colour x 10 ^colour  in Ohm’s (Ω) = 18x10⁹ Ω

3. Voltmeter should have extremely high internal resistance resistance so that electric current that passes through it, it should be extremely low and its effect can be neglected.

Ammeter should have very low internal resistance so that electric current can easily pass through as it is connected in series.
and the effect of resistance of ammeter should be negligible.

4. Here the thickness of bulb B is twice which means it cross-sectional area is 4 times of cross-sectional area of bulb A.
Hence resistance of bulb B is (1/4) times of resistance of bulb A

Hence current flowing through bulb B is 4 times as of bulb A
Which means bulb B will be 4 time brighter than bulb A