Electric Current Class 10 Science Notes, MCQs, Solved Examples, FAQs, Worksheet,Test Paper

ANAND CLASSES Study Material and Notes to explore detailed notes on Electric Current for Class 10, including concepts, FAQs, MCQs with answers, worksheets, and test papers. Perfect for CBSE, NEET & JEE preparation.

Electric Current- A Concept

Let’s begin with a simple question:

❓ What happens when you connect a wire between two charged bodies with different electric potentials?

Answer: Electric charges flow from the body with higher potential to the one with lower potential. This movement of electric charge is called electric current.

🌊 Analogy: Water Flow

Think of water stored in a tank. If we connect a pipe between a tank at a higher level and a lower one, water will naturally flow due to the difference in levels.
Likewise, charges flow due to the potential difference (voltage).

💡 Scientific Definition of Electric Current

Electric current is the rate at which electric charge flows through a conductor.

In mathematical form: $$I = \frac{Q}{t}$$

Where:

• I = Electric current (in amperes)
• Q = Total electric charge flowing (in coulombs)
• t = Time taken (in seconds)

🔌 What is Electric Current?

When two charged bodies at different electric potentials are connected using a metal wire, electric charges flow from the higher potential to the lower potential. This flow continues until both bodies reach the same potential.

• This movement of charges through a conductor constitutes electric current.
• The driving force behind this flow is the potential difference (also called voltage).

⚡ Definition:

Electric Current is the flow of electric charges (electrons) through a conductor such as a metal wire.

🔋 Why Does Current Flow in a Wire?

A metallic wire contains free electrons which are loosely held by atoms and can move easily.

🧲 When No Battery is Connected

• Electrons move randomly in all directions.
• The net current is zero.

🔋 When a Battery is Connected

• A potential difference (voltage) is applied.
• This creates an electric field in the wire.
• Electrons experience a force and drift slowly from the negative terminal to the positive terminal.
• This directional movement of electrons creates a current.

⚡ Direction of Electric Current

1. Conventional Current Direction

• Defined as the flow of positive charges from the positive terminal to the negative terminal.
• Established before electrons were discovered.

2. Actual Flow of Electrons

• In reality, electrons move from the negative terminal to the positive terminal.
• So, actual direction is opposite to the conventional direction.

🧪 SI Unit of Electric Current

The SI unit of current is the ampere (A). $$1~\text{ampere} = \frac{1~\text{coulomb}}{1~\text{second}}$$

🧾 Definition of Ampere:

If 1 coulomb of electric charge flows through a conductor in 1 second, the current is said to be 1 ampere.

🔍 Smaller Units of Electric Current

✨ Tip:

• Milli = $10^{-3}$ (one thousandth)
• Micro = $10−610^{-6}$ (one millionth)

🧰 How Do We Measure Current?

Current is measured by an instrument called ammeter. The ammeter is always connected in series with the circuit in which the current is to be measured.

For example, if we want to find out the current flowing through a conductor BC (such as a resistance wire), then we should connect the ammeter A in series with the conductor BC as shown in Figure. Since the entire current passes through the ammeter, therefore, an ammeter should have very
low resistance so that it may not change the value of the current flowing in the circuit.

🔧 Ammeter Properties:

• It is connected in series with the circuit element.
• Has very low resistance so it doesn’t affect the current flow.

🔁 Why ammeter is connected in Series With Circuit Elements?

Because same current flows through all components in a series connection.

🔎 Sample Problem – Electric Current

Q: An electric bulb draws a current of 0.25 A for 20 minutes. How much charge flows?

Solution:

Given:

• $I = 0.25~\text{A}$
• $t = 20~\text{min} = 20 \times 60 = 1200~\text{s}$

Using the formula: $$Q = I \times t = 0.25 \times 1200 = \boxed{300~\text{Coulombs}}$$

✅ So, 300 C of charge flows through the bulb in 20 minutes.

🔋 How to Maintain a Continuous Flow of Current?

You need to maintain a potential difference between two points. This is done using a cell or battery.

To maintain a potential difference between the two ends of a conductor so as to get a continuous flow of current is to connect the conductor between the terminals of a cell or a battery. Due to the chemical reactions going on inside the cell or battery, a potential difference is maintained between its terminals.

This potential difference drives the current in a circuit in which the cell or battery is connected. For example, a single dry cell has a potential difference of 1.5 volts between its two terminals (+ terminal and – terminal). So, when a dry cell is connected to a torch bulb through copper connecting wires, then its potential difference causes the electric current to flow through the copper wires and the bulb, due to which the bulb lights up (see Figure). In order to maintain current in the external circuit, the cell has to expend the chemical energy which is stored in it

🔄 Working of a Cell:

• Inside a battery, chemical reactions occur.
• These reactions maintain a potential difference between the positive and negative terminals.

This potential difference pushes electrons through the external circuit.

⚡ A cell “spends” chemical energy to maintain the flow of electric current.

🔥 Real-Life Example

When you insert a dry cell (1.5 V) into a torch and connect it to a bulb:

• The potential difference pushes electrons through the connecting wires and the filament of the bulb.
• This flow of electrons heats the filament, making it glow.

⚙️ What is Actually Happening Inside a Wire?

We know that electric current is a flow of electrons in a metal wire (or conductor) when a cell or battery is applied across its ends. A metal wire has plenty of free electrons in it.

Let’s go deeper into electron behavior:

(i) Before Battery is Connected

• Electrons move randomly.
• No net flow = No current.

When the metal wire has not been connected to a source of electricity like a cell or a battery, then the electrons present in it move at random in all the directions between the atoms of the metal wire as shown in Figure below.

(ii) After Battery is Connected

• Electric field is established.
• Electrons drift in the direction opposite to the field.
• This drift velocity creates electric current.

When a source of electricity like a cell or a battery is connected between the ends of the metal wire, then an electric force acts on the electrons present in the wire. Since the electrons are negatively charged, they start moving from
negative end to the positive end of the wire (see Figure). This flow of electrons constitutes the electric current in the wire.

🧪 Drift Velocity: Very slow — only a few mm/s.
Yet the effect of current is instantaneous because the electric field propagates at near light speed.

💡 Do You Know?

• Lightning carries thousands of amperes of current.
• The current in a mobile charger is about 1 to 2 A.
• Human nerves transmit electrical impulses of only microamperes.

🔌 Relation Between Electric Current and Number of Electrons Flow

The relation between electric current and charge is as follows :

$$I = \frac{Q}{t}$$

Where:

• I = Electric current (in amperes, A)
• Q = Total charge (in coulombs, C)
• t = Time (in seconds, s)

Now, charge Q is also related to the number of electrons by the formula: $$Q = n \times e$$

Where:

• n = Number of electrons
• e = Charge of one electron $= 1.6 \times 10^{-19} \, \text{C}$

🔄 Combining the Two Equations:

$$I = \frac{n \times e}{t}$$

📌 Final Formula:

$$\boxed{I = \frac{n \times e}{t}}$$

This is the relation between electric current (I), number of electrons (n), and time (t).

✅ Example: A current of 2 A flows through a conductor for 5 seconds. How many electrons flow through the conductor in this time?

Solution:

Step 1: Use the formula $$I = \frac{n \times e}{t} $$

$$ n = \frac{I \times t}{e}$$

Step 2: Plug in the values $$I = 2 \, \text{A}, \quad t = 5 \, \text{s}, \quad e = 1.6 \times 10^{-19} \, \text{C} $$

$$n = \frac{2 \times 5}{1.6 \times 10^{-19}} $$

$$n = \frac{10}{1.6 \times 10^{-19}} $$

$$n = 6.25 \times 10^{19} \, \text{electrons}$$

✅ Answer:

$\boxed{6.25 \times 10^{19} \, \text{electrons}}$ flow through the conductor in 5 seconds.

❓ Frequently Asked Questions (FAQs)

Q1. What is the SI unit of electric current?

A: The SI unit is ampere (A).

Q2. What causes electric current to flow?

A: The potential difference (voltage) between two points.

Q3. Which particles are responsible for electric current in a wire?

A: Electrons.

Q4. What is the direction of current flow?

A: Conventional current flows from positive to negative; electron flow is the opposite.

🔍 Conceptual Questions with Answers

Q1. Why is the ammeter connected in series, not in parallel?

A: Because it must measure the actual current flowing through the component, and if connected in parallel, it may get damaged due to low resistance.

Q2. Why do electrons move in a specific direction when a cell is connected?

A: The electric field created by the cell exerts force on electrons, pushing them from negative to positive.

Q3. If 1 A current flows through a wire, how many electrons pass per second?

$$\text{Charge of one electron} = 1.6 \times 10^{-19} C$$

$$\text{Number of electrons} = \frac{1}{1.6 \times 10^{-19}} \approx 6.25 \times 10^{18} \text{ electrons/sec}$$

🧠 MCQs with Explanation

Q1. What is the SI unit of electric current?
A. Volt
B. Ampere ✅
C. Coulomb
D. Ohm
Explanation: Ampere is the standard SI unit.

Q2. 1 mA is equal to:
A. 0.001 A ✅
B. 0.1 A
C. 10⁻⁶ A
D. 1 A
Explanation: 1 milliampere = 10⁻³ A

Q3. Electrons in a conductor move from:
A. Positive to Negative
B. Neutral to Negative
C. Negative to Positive ✅
D. Stationary
Explanation: Electrons are negatively charged, so they move from negative to positive.

💡 Do You Know?

• A lightning bolt carries current of around 30,000 A!
• The human body can detect currents as low as 1 mA.
• In metallic conductors, only electrons move—not protons!

📄 Worksheet: Practice Questions

Fill in the blanks:

1. Electric current is the flow of __________.
2. SI unit of current is __________.
3. Direction of conventional current is from __________ to __________ terminal.
4. Electrons flow from __________ to __________ terminal.

True/False:

1. Ammeter is connected in parallel. ❌
2. Electron flow and conventional current flow in the same direction. ❌
3. 1 A = 1000 mA. ✅

📝 Test Paper (Marks: 25)

Section A: Very Short Answer (1 Mark each)

1. Define electric current.
2. Write the formula for current.
3. What is the SI unit of current?
4. Define 1 ampere.

Section B: Short Answer (2 Marks each)

5. Why is an ammeter connected in series?
6. Differentiate between conventional current and electron flow.
7. Convert 500 mA into amperes.

Section C: Long Answer (3 Marks each)

8. Describe how current flows in a wire when a battery is connected.
9. A torch bulb draws 0.5 A current for 10 minutes. Calculate the total charge passed.
10. Explain with a diagram how potential difference causes current in a circuit.

🧾 Important Points for Quick Revision

✅ Electric current = flow of electrons
✅ SI unit = Ampere (A)
✅ Formula: $I = \frac{Q}{t}$
✅ 1 A = 1 C/s
✅ 1 mA = $10^{-3}$
✅ 1 µA = $10^{-6}$
✅ Current flows due to potential difference
✅ Conventional current: + to –
✅ Electron flow: – to +
✅ Ammeter is connected in series

📝 Summary – Quick Revision Table