Key Notes
Electricity
Current:
I = Q/t, Where I = Current
Q = Net charge flowing.
t = time
• Unit:
The unit of current is Ampere.
Q = Coulomb(C)
I = Ampere(A)
t = Second(s) 1 A = 1C/1s
Potential Difference:
The potential difference between two separate points is defined as the work done to move a unit positive charge from one point to another.
V = W/Q
• Unit:
The unit of potential difference is Volt
1 Volt = 1 Joule/ 1 Coulomb
Ohm’s Law:
Current ∝ potential difference
V ∝ I
V = I R where, R = Resistance
• Unit:
R = Ω(Ohm)
1Ω = 1V / 1 A
• Factors on which resistance depends:
○ R ∝ 1, when A and material constant l = length
○ R ∝ 1/ A, when l and material constant A = perpendicular cross-section
R ∝l / A,
R = ρl / A, where ρ = resistivity
• Resistivity: Resistivity of a substance is equal to the resistance of a unit square of that substance.
Its Unitis Ωm.
Resistance in a series connection:
R = R1 + R2 + R3 + … + Rn
Resistance in parallel:
Heating Effect of current:
Electric energy = VIt
Heat, H = VIt = I2Rt
• Application:
Electric iron, toaster, fused wire, etc.
Fused wire: a low-melting point wire connected in series with electric devices for safety.
Electric power:
• Unit: 1 kWh = 3.6 × 106J
1 W = 1V × 1A
Ohm’ law: Under constant physical conditions (i.e., constant temperature, pressure etc.), the current flowing through a conductor is directly proportional to the potential difference across the conductor.
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Potential difference (which is measured in Voltage) is the cause of current (which is measured in Ampere).
![](/cbse-ncert/class-10/10-sci-phy-2-UntitOE0.JPG)
In conductors, flow of electrons constitute current. In a circuit current flow from positive terminal of the battery to the negative terminal, but electrons travels from negative terminal to the positive terminal. The negative terminal of a battery is said to be at lower potential and the positive terminal is said to be at higher potential.
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When a battery is not connected to any circuit, the potential difference across the terminals of the battery is equal to the EMF of the battery. (EMF = Electro Motive Force). Electromotive force, also called EMF, (denoted and measured in volts), refers to voltage generated by a battery or by the magnetic forceaccording to Faraday's Law, which states that a time varying magnetic field will induce an electric current.