📘 Class 10 Science: Electricity (Easy Notes)

               1. Electric Charge 

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• Electric Charge (Q):
  • A fundamental property of matter that causes particles to experience electrical forces.
  • Two types: Positive and Negative.
  • Unit: Coulomb (C).
• Behavior:
  • Like charges repel each other.
  • Unlike charges attract each other.
• Formula: Q=n⋅e where  Q= total charge, 

         n= number of electrons (or charged particles),

         e= charge of one electron =1.6×10−19C

So, if you know how many electrons are transferred, you can calculate the total charge.

2. Electric Current 

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• Definition: Electric current is the rate of flow of electric charge through a conductor. It tells us how fast electrons are moving in a wire or circuit.
• Formula: I=Qt

I = Electric current (in amperes)
Q = Total charge (in coulombs) , t = Time (in seconds)
This formula shows that current increases if more charge flows in less time.

• Unit: Ampere (A) is the SI unit of current.
• Defined as: 1A=1C1s1A = \frac{1C}{1s}

         → If 1 coulomb of charge flows in 1 second, the current is 1 ampere.

• Measurement Tip:
  • An ammeter is used to measure current.
  • It is always connected in series in the circuit so that the same current flows through it.

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   3. Electric Circuit 

• Definition: An electric circuit is a closed path through which electric current flows. If the path is broken (open), current cannot flow.
• Symbols Used in Circuit Diagrams: These are standardized symbols used to represent components:
  • Cell → single power source
  • Battery → multiple cells connected
  • Bulb → load or output device
  • Switch → control element (open/closed)
  • Wire → conducting path

“These symbols are used in CBSE circuit diagrams to simplify and standardize representation. “

• Direction of Current: Conventional Current: Flows from positive (+) to negative (–) terminal. This is the direction assumed in textbooks and diagrams.Electronic Current: Actual flow of electrons, which move from negative (–) to positive (+). This is the physical reality inside conductors.

📚 Page Context

This explanation is part of your step-by-step visual summary for students. It helps them understand:

• What a circuit is
• How to read and draw circuit diagrams
• The difference between assumed current flow and actual electron movement

This is especially useful for CBSE exam questions that ask students to draw or interpret circuits, and for practical understanding in labs.
4. Ohm’s Law Statement: 

 Ohm’s Law states that the electric current (I) flowing through a conductor is directly proportional to the voltage (V) across it, provided the temperature remains constant.

• Mathematical Form: 

V∝I⇒V=I⋅R

• VV = Voltage (in volts)
• II = Current (in amperes)
• RR = Resistance (in ohms, Ω)

• Resistance (R):It is the property of a conductor that opposes the flow of current. Higher resistance → less current for the same voltage.
• Graphical Representation:
  • A V–I graph (Voltage vs Current) for a conductor obeying Ohm’s Law is a straight line.
  • The slope of the line gives the resistance of the conductor.

📚 Page Context

This explanation is part of your step-by-step visual summary for CBSE students. It helps them:

• Understand the relationship between voltage, current, and resistance
• Apply the formula V=IRV = IR in numerical problems
• Interpret graphs in exams and lab experiments

This concept is frequently tested in CBSE exams through numerical questions, graph interpretation, and circuit analysis.

🧮 CBSE Board Numerical Questions – Ohm’s Law

🔹 Question 1

A current of 2A flows through a resistor of 5Ω. What is the potential difference across the resistor?

Solution:

V=I⋅R=2⋅5=10VV = I \cdot R = 2 \cdot 5 = 10V

Answer: 10 Volts

🔹 Question 2

If a 12V battery is connected across a resistor and the current is 3A, find the resistance.

Solution:

R=VI=123=4ΩR = \frac{V}{I} = \frac{12}{3} = 4Ω

Answer: 4 Ohms

🔹 Question 3

A wire has resistance of 10Ω. How much current will flow if 20V is applied?

Solution:

I=VR=2010=2AI = \frac{V}{R} = \frac{20}{10} = 2A

Answer: 2 Ampere

🔹 Question 4

A bulb draws 0.5A current when connected to a 220V supply. What is its resistance?

Solution:

R=VI=2200.5=440ΩR = \frac{V}{I} = \frac{220}{0.5} = 440Ω

Answer: 440 Ohms

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5. Factor affecting Resistance 

🔎 Concept Breakdown: Resistance and Its Influencing Factors:

• Resistance (R): It is the property of a conductor that opposes the flow of electric current. Measured in Ohms (Ω).

📊 Factors Affecting Resistance

Factor	Effect on Resistance
Length (L)	Resistance increases with length → R∝LR \propto L
Area of Cross-section (A)	Resistance decreases with area → R∝1AR \propto \frac{1}{A}
Temperature	Resistance increases with temperature (especially in metals)
Nature of Material	Insulators & conductors have high and low resistance

• Formula for Resistance

R=ρ⋅LA

• RR = Resistance
• ρ\rho = Resistivity of the material (depends on nature of material)
• LL = Length of the conductor
• AA = Area of cross-section

                    ” This formula shows how geometry and material affect resistance.”

📚 Page Context

This section is part of your step-by-step visual summary for CBSE students. It helps them:

• Understand how wire dimensions and material choice affect resistance
• Apply the formula in numerical problems
• Interpret graphs and tables in exams and lab experiments