【People's Education Press】High School Physics - Required Course, Volume 3: Energy Transformation: From Everyday Phenomena to Physical Principles

Electric energy is not only the cornerstone of modern civilization but also the universal currency of natural energy transformationuniversal currency. The core logic of this lesson starts from macroscopic everyday electrical appliances, observing how electrical energy transforms into mechanical, thermal, light, and chemical energy, to understandthe physical essence that "work is the measure of energy transformation"this fundamental physical principle.

Core Mechanisms

Electrical Work and Conversion: The process of current doing work is equivalent to the conversion of electrical energy into other forms. Motors primarily convert electrical energy into mechanical energy, but in non-ohmic circuits, internal resistance also generates thermal energy.
System Conservation View: Energy cannot be created from nothing. For example, the Hualong One nuclear power plant converts nuclear fission energy into thermal energy, which drives turbines to produce mechanical energy, finally generating electricity through a generator.
Efficiency Evaluation: Actual conversions always involve losses. For instance, when a desktop fan operates, input power $P$ is converted into useful work $P_{mech}$ and thermal loss $I^2R$.

QUESTION 1

[Short Answer] In Figure 11-1, the voltage $U$ between points $A$ and $B$ is $10\,\text{V}$. Resistors are $R_1 = 1\,\text{k}\Omega$, $R_2 = 5\,\Omega$, $R_3 = 2\,\text{k}\Omega$, and $R_4 = 10\,\text{k}\Omega$. Estimate the current $I$ in the main circuit.

0.5 A

2 A

5 A

10 A

QUESTION 2

[Short Answer] [Image: Circuit 11.4-7] In the circuit shown in Figure 11.4-7, the voltage between points $A$ and $B$ is $U$. The fixed resistor has resistance $R$, and the maximum resistance of the variable resistor is $R_1$. What is the range of voltage $U_R$ across resistor $R$ as the slider moves?

0 to $U$

$U \frac{R}{R+R_1}$ to $U$

$U \frac{R_1}{R+R_1}$ to $U$

QUESTION 3

[Short Answer] [Image: Circuit 12.1-5] Four fixed resistors are connected as shown in Figure 12.1-5. $R_A$ and $R_C$ are rated at "10 V, 4 W", and $R_B$ and $R_D$ at "10 V, 2 W". Arrange these four resistors by their power consumption in descending order.

$P_B = P_D > P_A = P_C$

$P_A = P_C > P_B = P_D$

$P_A = P_B = P_C = P_D$

QUESTION 4

In a purely resistive circuit, what is the relationship between electrical work $W$ and generated Joule heat $Q$?

$W > Q$

$W = Q$

$W < Q$

QUESTION 5

When a motor operates, if the total input power is $P$ and the output mechanical power is $P_{out}$, what is the power dissipated as heat due to internal resistance?

$P + P_{out}$

$P - P_{out}$

$P \cdot P_{out}$