ELECTRIC CURRENT, CIRCUITS AND OHM'S LAW IMPORTANT NOTES ( CBSE 10TH SCIENCE )

 

1. Electric Current

• Definition: The rate of flow of electric charge through a conductor.

  $$\mathrm{<span\; style="font-size:\; medium;"><b>I</b></span>}<span\; style="font-size:\; medium;"><b>=</b></span>\frac{\mathrm{<span\; style="font-size:\; medium;"><b>Q</b></span>}}{\mathrm{<span\; style="font-size:\; medium;"><b>t</b></span>}}$$

  where
  $I$= current (ampere, A)
  $Q$ = charge (coulombs, C)
  $t$= time (seconds, s)

• Direction:
  Conventional current flows from positive → negative terminal of a cell.
  Electron flow is actually from negative → positive.

• Unit Conversion:
  1 A = 1 C/s.

2.Electric Potential & Potential Difference

• Potential difference (V): Work done to move a unit positive charge between two points.

  V=W/Q​​

  Unit: Volt (V)
  1 V = 1 Joule/Coulomb

3. Electric Circuit

• Closed path for current flow, made of:

  • Source (cell/battery)

  • Conductors (wires)

  • Load (bulb/resistor)

  • Switch (to open/close circuit)

• Symbols to learn (for diagram-based questions):

  • Cell, battery, wire, key/switch (open & closed), resistor, variable resistor (rheostat), ammeter, voltmeter, galvanometer, etc.

 4.Ohm’s Law

• Statement: At constant temperature, the current (I) through a conductor is directly proportional to the potential difference (V) across it.

  $$\mathrm{<br>}$$

  $R$ = resistance (Ω).

• Resistance (R):

  R=ρl/A​​

  $\rho$= resistivity of material (Ω·m)
  $l$= length of conductor (m)
  $A$= cross-sectional area (m²)

• Graph:

  • Plot V (y-axis) vs I (x-axis) → straight line through origin.

  • Slope = Resistance $R$.

• 5. Series and Parallel Circuits

  • Series: $R_{\text{eq}} = R_1 + R_2 + R_3 + \dots$

    • Same current flows, voltage divides.

  • Parallel: $\frac{1}{R_{\text{eq}}} = \frac{1}{R_1} + \frac{1}{R_2} + \dots$

    • Same voltage across branches, current divides.

6. Electric Power

• $$P=VI=I^2\mathrm{R\; , }$$

  Unit: Watt (W)
  1 kW = 1000 W.

• Key Points for CBSE Exam

  • Always label circuit diagrams (Ammeter in series, Voltmeter in parallel).

  • Temperature constant condition is important in Ohm’s Law questions.

  • Practice numericals using:

    • $V = IR$
      

    • $P =$ $P = V2/R$​

  • Remember units and conversions (e.g., 1 mA = ${10}^{-\mathrm{3A}}$).