Checking Up 1. What unit does the pover company use to charge consumes for energy? 2. If a sudent leaves a 100-W light bulb on in his room for it h how mary kilowatt-hours of electricty does the bulb use? If the power company charges $$ \$ 0.18 $$ per kilowatt-hour, how mudh will it cost to leave the light bulb on for this amount of time? 3. List two places where you could bok to see how much electrial energy your family has used in the previous month 4. What is the name given to heat transfer when objects are heated by direct contact? By cuments flowing through a fluid? By electromagnetic woves? 5. When objects are heated by contact, what happens to the kinetic energy of the cold molecules in contact with the hot heating coil? 6. What happens to the distance between molecules in a fluid as their temperature increases?

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### 1. **What unit does the power company use to charge consumers for energy?**

**Answer:**  
Power companies typically charge consumers based on the amount of electrical energy they consume, measured in **kilowatt-hours (kWh)**.

- **Kilowatt-hour (kWh):**  
  - **Kilowatt (kW):** A unit of power equal to 1,000 watts.
  - **Hour (h):** A unit of time.
  - **kWh:** Represents the energy usage of 1,000 watts over the period of one hour.

**Example:**  
If you use a 1,000-watt appliance for one hour, you will consume 1 kWh of energy.

---

### 2. **Energy Consumption and Cost of Operating a 100-Watt Light Bulb**

**Question:**  
If a student leaves a 100-W light bulb on in his room for **how many** kilowatt-hours of electricity does the bulb use? If the power company charges **$0.18** per kilowatt-hour, how much will it cost to leave the light bulb on for this amount of time?

**Assumptions:**  
It seems there's a typo in the question regarding the duration. Commonly, such problems assume a duration of **one hour**. I'll proceed with that assumption.

**Calculations:**

1. **Convert Watts to Kilowatts:**
   $$
   100\ \text{W} = 0.1\ \text{kW}
   $$

2. **Calculate Energy Consumed (in kWh):**
   $$
   \text{Energy} = \text{Power} \times \text{Time} = 0.1\ \text{kW} \times 1\ \text{hour} = 0.1\ \text{kWh}
   $$

3. **Calculate Cost:**
   $$
   \text{Cost} = \text{Energy} \times \text{Rate} = 0.1\ \text{kWh} \times \$0.18/\text{kWh} = \$0.018
   $$

**Answer:**  
The 100-W light bulb uses **0.1 kilowatt-hours (kWh)** of electricity when left on for one hour. At a rate of **$0.18 per kWh**, it costs **$0.018** (or 1.8 cents) to operate the bulb for one hour.

---

### 3. **Places to Check Your Family's Electrical Energy Usage**

**Answer:**  
You can check how much electrical energy your family has used in the previous month by looking at:

1. **Electricity Bill Statement:**  
   - **Description:** Monthly statements provided by your power company detail the total energy consumption in kWh for each billing period.
   - **Access:** Sent via mail, email, or available through the power company's online portal.

2. **Electric Meter Readings:**  
   - **Description:** Reading your home's electric meter allows you to track your energy usage.
   - **Access:** Locate your home's electric meter (usually outside or in a utility area), record the numbers at the start and end of the month, and calculate the difference.

**Additional Option:**  
- **Smart Meters or Home Energy Monitors:** Some homes are equipped with smart meters or devices that provide real-time energy usage data, accessible through apps or online dashboards.

---

### 4. **Names of Heat Transfer Methods**

**Answer:**  
Heat can be transferred in three primary ways:

1. **By Direct Contact:** **Conduction**  
   - **Description:** Transfer of heat through a material by direct contact of its particles. Example: A metal spoon heating up in a pot of hot soup.

2. **By Currents Flowing Through a Fluid:** **Convection**  
   - **Description:** Transfer of heat by the movement of a fluid (liquid or gas). Example: Boiling water where hot water rises and cool water descends, creating a convection current.

3. **By Electromagnetic Waves:** **Radiation**  
   - **Description:** Transfer of heat through electromagnetic waves without needing a medium. Example: Heat from the Sun reaching the Earth.

---

### 5. **Effect on Kinetic Energy of Cold Molecules in Contact with a Hot Heating Coil**

**Answer:**  
When objects are heated by direct contact (conduction), the **cold molecules** in contact with the **hot heating coil** **absorb energy**, causing their **kinetic energy to increase**. This results in the molecules moving more rapidly, which can lead to a temperature rise in the previously cold material.

**Explanation:**
- **Kinetic Energy Increase:**  
  - The transfer of thermal energy from the hot coil to the cold molecules increases the vibration and movement of these molecules.
  - As their kinetic energy increases, the temperature of the cold material rises until thermal equilibrium is reached.

---

### 6. **Effect of Temperature Increase on the Distance Between Molecules in a Fluid**

**Answer:**  
As the **temperature of a fluid increases**, the **distance between its molecules generally **increases**.

**Explanation:**
- **Molecular Movement:**  
  - Higher temperatures provide molecules with more kinetic energy, causing them to move more vigorously.
  
- **Resulting Expansion:**  
  - Increased molecular movement causes the molecules to occupy more space, leading to the expansion of the fluid.
  
- **Implications:**  
  - This is why most fluids expand when heated and contract when cooled.

---

Feel free to ask if you have any more questions or need further clarification on any of these topics!
1. **Power companies charge consumers in kilowatt-hours (kWh).** 2. **A 100-W light bulb uses 0.1 kWh in one hour. At $0.18 per kWh, it costs $0.018 (1.8 cents) to leave it on for one hour.** 3. **Check your electricity bill or use a smart meter to see your family's energy usage.** 4. **Heat transfer by direct contact is called conduction. By currents flowing through a fluid is convection. By electromagnetic waves is radiation.** 5. **When cold molecules are heated by a hot coil, their kinetic energy increases.** 6. **As temperature increases, the distance between molecules in a fluid generally increases.**

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