Question 1

A potentiometer wire of length 1.00 m is connected across a 4.0 V driver cell. What is the potential difference across each 1 cm length of the wire?

Accepted Answer

$$0.04\ \mathrm{V}$$

Question 2

If a cell of unknown e.m.f. $$E$$ gives a balance point at $$37.0\ \mathrm{cm} on $$the potentiometer wire (total length $$100\ \mathrm{cm}$$, total p.d. $$4.0\ \mathrm{V}$$), what is the estimated value of $$E$$?

Accepted Answer

$$1.48\ \mathrm{V}$$

Question 3

Why is the value of $$E$$ found in the previous question only an estimate?

Accepted Answer

Because the potentiometer wire may not have uniform resistance or the driver cell may have internal resistance.

Question 4

A standard cell of e.m.f. $$1.230\ \mathrm{V}$$ gives a balance length of $$31.2\ \mathrm{cm} on $$the same potentiometer. If the unknown cell gives a balance length of $$37.0\ \mathrm{cm}$$, what is the more accurate value for $$E$$?

Accepted Answer

$$1.46\ \mathrm{V}$$

Question 5

In the potentiometer circuit shown, a student cannot find a balance point using the test cell. What is the most likely reason?

Accepted Answer

The e.m.f. of the test cell is greater than the driver cell.

Question 6

How would the student recognize the balance point in a potentiometer experiment?

Accepted Answer

When the voltmeter or galvanometer shows zero reading.

Question 7

A test cell gives a balance length of $$22.5\ \mathrm{cm}$$ and a standard cell of $$1.434\ \mathrm{V}$$ gives $$34.6\ \mathrm{cm}. $$What is the e.m.f. of the test cell?

Accepted Answer

$$0.932\ \mathrm{V}$$

Question 8

In a potential divider circuit with $$R_1 ($$variable) and $$R_2 = 470$$\ \Omega$$, the battery is 9.0$$\ \mathrm{V}$$. What is the value of R_1$ when the voltmeter reads 2.0$$\ \mathrm{V}$$ across R_2$?

Accepted Answer

$$1645\ \Omega$$

Question 9

If the voltmeter in the potential divider circuit is replaced with one of resistance $$2\ \mathrm{k}\Omega$$, what will the new reading be (across $$R_2 = 470$$\ \Omega$$ and R_1$ = 1645\ \Omega$$)?

Accepted Answer

$$1.67\ \mathrm{V}$$

Question 10

A lamp is rated at $$60\ \mathrm{W} at$$ $$240\ \mathrm{V}. $$What is the resistance of the lamp filament at its normal operating temperature?

Accepted Answer

$$960\ \Omega$$

Question 11

How does the resistance of a lamp filament at room temperature compare to its resistance at normal operating temperature?

Accepted Answer

It is lower at room temperature because resistance increases with temperature for metals.

Question 12

In a potential divider, what happens to the voltmeter reading across $$R_2 if $$the resistance of the variable resistor $$R_1 is $$increased?

Accepted Answer

The voltmeter reading decreases.

Question 13

A potentiometer is used to compare the resistances of two resistors. If $$R_1$$ alone gives a balance length of $$15.4\ \mathrm{cm}$$ and $$R_1$$ and $$R_2 in $$series give $$42.6\ \mathrm{cm}$$, what is the ratio $$\frac{R_1$}{R_1$ + R_2$}$$?

Accepted Answer

$$0.362$$

Question 14

Given the same data as above, what is the ratio $$\frac{R_1$}{R_2$}$$?

Accepted Answer

$$0.568$$

Question 15

If the uncertainty in measuring the balance length is $$0.2\ \mathrm{cm}$$ for both $$R_1$$ and $$R_1$$ + $$R_2$$, what is the uncertainty in the ratio $$\frac{R_1$}{R_2$}$$?

Accepted Answer

$$0.02$$

Question 16

Which of the following best explains why a potentiometer is more accurate than a voltmeter for measuring e.m.f.?

Accepted Answer

A potentiometer measures e.m.f. without drawing current from the cell.

Question 17

In a dimmer switch circuit, what is one advantage of using a variable resistor in series with the lamp (circuit 1) compared to a parallel arrangement (circuit 2)?

Accepted Answer

It allows for smoother and more efficient control of brightness.

Potentiometers, EMF Comparison, and Potential Divider Circuits – SW2

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