GCSE Physics - Charge, Current & Time #16

Summary

This video explains the concept of electric charge and how to calculate it. Charge, measured in coulombs (C), is the total current that flows over a period of time. The equation provided is Q = I × t, where Q is charge, I is current (in amps), and t is time (in seconds). The video walks through two example problems: calculating charge from current and time, and determining current from charge and time, while converting units when needed. The explanation is simple and supported by relatable examples.

Takeaways

• ⚡ Charge is a measure of the total current that flows over a certain period of time.
• 🌊 Charge can be compared to the total amount of water that flows through a river over time.
• 🔤 Charge is represented by the letter 'q' and measured in coulombs (C).
• 🧮 The equation for charge is: Charge (q) = Current (I) × Time (t), with current in amps and time in seconds.
• ☕ Example: A kettle with a 12-amp current over 50 seconds results in 600 coulombs of charge (12 × 50).
• 📱 Example: For a phone charger transferring 43.2 kilocoulombs over 2 hours, the current is calculated by rearranging the equation to I = q / t.
• 🔄 To solve for current, divide charge by time: I = q / t.
• 🔢 Convert units when needed, such as kilocoulombs to coulombs or hours to seconds, for accurate calculations.
• 📏 In the second example, 43.2 kilocoulombs is 43,200 coulombs, and 2 hours is 7,200 seconds.
• 💡 The final calculation for the phone charger example gives a current of 6 amps (43,200 ÷ 7,200).

Q & A

What is the definition of charge in the context of electrical circuits?

Charge is a measure of the total current that flowed within a certain period of time.

What analogy is used in the video to explain current and charge?

The water analogy is used, where current is the rate at which water flows through a river, and charge is the total amount of water that has flowed down the hill within a certain time frame.

What letter is used to represent charge, and in what unit is it measured?

Charge is represented by the letter 'Q' and is measured in coulombs (C).

What is the formula used to calculate charge?

The formula for charge is: Charge (Q) = Current (I) × Time (T), where current is in amps and time is in seconds.

In the example of a kettle drawing 12 amps of current and taking 50 seconds to boil, how much charge passes through the wire?

The charge is calculated as 12 amps × 50 seconds = 600 coulombs.

What is the rearranged formula to calculate current if charge and time are known?

The formula for current is rearranged as: Current (I) = Charge (Q) / Time (T).

How do you convert kilocoulombs to coulombs?

To convert kilocoulombs to coulombs, multiply the value in kilocoulombs by 1,000.

In the phone charger example, how do you convert hours into seconds?

To convert hours into seconds, multiply the number of hours by 60 to get minutes, and then multiply by 60 again to get seconds. For example, 2 hours × 60 × 60 = 7,200 seconds.

How much current flowed through the wire in the phone charger example where 43.2 kilocoulombs were transferred over 2 hours?

The current is calculated as 43,200 coulombs / 7,200 seconds = 6 amps.

Why is it important to convert units before calculating current or charge in these examples?

Converting units ensures that all values are in the correct base units (coulombs for charge, seconds for time, amps for current) so that the calculations are accurate.