Q: A 10 F capacitor is charged to a potential difference of 3 V. How much energy is stored in the capacitor?

$$\frac{1}{2}CV^2$ = \frac{1}{2} \times 10 \times 3^2$ = 45\ \text{J}$$

Q: Which equation correctly describes the energy density stored in the electric field of a capacitor?

$$\text{Energy density} = \frac{1}{2} \kappa \$$varepsilon_0$$ E^2$

Q: A current of 0.17 mA flows for one hour in a calculator circuit. How much charge passes through the circuit?

$$q = I \Delta t = 0.17 \times 10$$^{-3}$$ \times 3600 = 0.61\ \text{C}$$

Q: A 35 m long 20-gauge copper wire has a cross-sectional area of $$5.2 \times 10$$^{-7}$$\ \text{m}^2$$ and a resistivity of $$1.72 \times 10$$^{-8}$$\ \Omega\cdot\text{m}. $$What is its resistance?

$$R = \frac{\rho L}{A} = \frac{1.72 \times 10$$^{-8}$$ \times 35}{5.2 \times 10$$^{-7}$$} = 2.1\ \Omega$$

Q: A heating element has a resistivity of $$6.8 \times 10$$^{-5}$$\ \Omega\cdot\text{m} at$$ $$320^\circC $$and a temperature coefficient of $$2.0 \times 10$$^{-3}$$\ (\text{C}^{-1}). $$What is its resistivity at $$420^\circC$$?

$$\rho = \$$rho_0$$ [1 + \alpha (T - T_0$)] = 6.8 \times 10$$^{-5}$$ [1 + 2.0 \times 10$$^{-3}$$ \times (420 - 320)] = 8.2 \times 10$$^{-5}$$\ \Omega\cdot\text{m}$$

Q: If the voltage across a heating element is 120 V and its resistance at $$420^\circC is$$ $$29\ \Omega$$, what is the current drawn?

$$I = \frac{V}{R} = \frac{120}{29} = 4.1\ \text{A}$$

Q: Which material would be best for making a wire with minimal resistance, based on the table of resistivities?

Silver ($$\rho = 1.59 \times 10$$^{-8}$$\ \Omega\cdot\text{m})$$

Question 1

A 10 F capacitor is charged to a potential difference of 3 V. How much energy is stored in the capacitor?

Accepted Answer

$$\frac{1}{2}CV^2$ = \frac{1}{2} 	imes 10 	imes 3^2$ = 45\ 	ext{J}$$

Question 2

Which equation correctly describes the energy density stored in the electric field of a capacitor?

Accepted Answer

$$	ext{Energy density} = \frac{1}{2} \kappa \$$varepsilon_0$$ E^2$

Question 3

A battery provides a maximum potential difference of 12 V. What is this value called?

Accepted Answer

Electromotive force (emf)

Question 4

In a Zn-Cu cell with dilute H$$_2SO$_4$$, what is the role of zinc?

Accepted Answer

Zinc acts as the anode, releasing electrons and forming Zn$$^{2+}$$ ions.

Question 5

A current of 0.17 mA flows for one hour in a calculator circuit. How much charge passes through the circuit?

Accepted Answer

$$q = I \Delta t = 0.17 	imes 10$$^{-3}$$ 	imes 3600 = 0.61\ 	ext{C}$$

Question 6

Which statement best describes conventional current?

Accepted Answer

Conventional current is the hypothetical flow of positive charges, opposite to electron flow.

Question 7

A flashlight uses two 1.5-V batteries and provides a current of 0.40 A. What is the resistance of the bulb filament?

Accepted Answer

Question 8

Which equation gives the resistance of a wire in terms of its length $$L$$, cross-sectional area $$A$$, and resistivity $$\rho$$?

Accepted Answer

$$R = \frac{\rho L}{A}$$

Question 9

A 35 m long 20-gauge copper wire has a cross-sectional area of $$5.2 	imes 10$$^{-7}$$\ 	ext{m}^2$$ and a resistivity of $$1.72 	imes 10$$^{-8}$$\ \Omega\cdot	ext{m}. $$What is its resistance?

Accepted Answer

$$R = \frac{ho L}{A} = \frac{1.72 	imes 10$$^{-8}$$ 	imes 35}{5.2 	imes 10$$^{-7}$$} = 2.1\ \Omega$$

Question 10

How does increasing the length of a wire affect its resistance, assuming all other factors remain constant?

Accepted Answer

Resistance increases linearly with length.

Question 11

A heating element has a resistivity of $$6.8 	imes 10$$^{-5}$$\ \Omega\cdot	ext{m} at$$ $$320^\circC $$and a temperature coefficient of $$2.0 	imes 10$$^{-3}$$\ (	ext{C}^{-1}). $$What is its resistivity at $$420^\circC$$?

Accepted Answer

$$ho = \$$rho_0$$ [1 + \alpha (T - T_0$)] = 6.8 	imes 10$$^{-5}$$ [1 + 2.0 	imes 10$$^{-3}$$ 	imes (420 - 320)] = 8.2 	imes 10$$^{-5}$$\ \Omega\cdot	ext{m}$$

Question 12

If the voltage across a heating element is 120 V and its resistance at $$420^\circC is$$ $$29\ \Omega$$, what is the current drawn?

Accepted Answer

$$I = \frac{V}{R} = \frac{120}{29} = 4.1\ 	ext{A}$$

Question 13

Which material would be best for making a wire with minimal resistance, based on the table of resistivities?

Accepted Answer

Silver ($$ho = 1.59 	imes 10$$^{-8}$$\ \Omega\cdot	ext{m})$$

Question 14

What happens to the resistance of a wire if its cross-sectional area is doubled, keeping length and material constant?

Accepted Answer

Resistance is halved.

Question 15

Which of the following statements about superconductors is correct?

Accepted Answer

Superconductors have zero resistance below a critical temperature.

Question 16

A wire is heated from $$20^\circC to$$ $$120^\circC. If $$its temperature coefficient of resistivity is $$0.004\ (	ext{C}^{-1})$$, by what factor does its resistivity increase?

Accepted Answer

$$1 + \alpha (T - T_0$) = 1 + 0.004 	imes (120 - 20) = 1.4$$

Question 17

Which of the following best describes the relationship between voltage, current, and resistance in Ohm's Law?

Accepted Answer

$$V = IR$$

Question 18

A device is connected to a battery. Which direction does conventional current flow relative to electron flow?

Accepted Answer

Conventional current flows from the positive terminal to the negative terminal, opposite to electron flow.

lec 6

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