Summary & Quick Quiz ധാരാവൈദ്യുതി
The whole chapter on one page: the key boxes of the textbook, every formula, unit and circuit symbol you need, the mistakes to avoid, flashcards, a scored quiz and your study checklist.
1. The chapter in one picture
Read it clockwise from the top left: a source keeps a potential difference; the potential difference makes charge flow – a current; Ohm’s law links them through the resistance; resistance depends on the wire; and cells and resistors can be combined in series or in parallel. In the middle: the simplest circuit, with the current flowing from + to − outside the cell.
2. The key boxes of the textbook
Stores electrical energy and, when needed, supplies a current for a short time by discharging. Used in almost all electronic devices. A cell, instead, keeps a current going continuously. – page 5
The flow of charges through a circuit creates an electric current. – page 5
The work done to move a unit charge from one point to another in a circuit. Electric potential = the potential energy of a unit charge at a point. – page 5
A source used to maintain a potential difference between two points of a circuit – like a pump keeping a water-level difference. – page 5
emf: the potential difference between the terminals of a source when no current is drawn – the most it can give. Unit J/C = volt; 1 V = 1 J of work per coulomb. – page 5
Italy, 1745–1827. Invented the electric cell (voltaic pile); discovered methane; professor at Pavia. The volt is named after him. – page 6
Primary cells cannot be reused (dry cell, button cell); secondary (storage) cells can be recharged (mobile, car, inverter battery). A battery = several cells working as one source. – page 6
+ of one cell to − of the next: the emfs add. Two 1.5 V cells → 3 V; four → 6 V. – page 6
Identical cells + to +, − to −: the same emf as one cell, but the current lasts longer (power banks, mobile phones). Two cells joined + to + give 0 V – never do it. – page 6
The charge flowing per unit time. Unit C/s = ampere, after André-Marie Ampère (France, 1775–1836, began electromagnetism). 1 A = 1000 mA; 1 mA = 1000 µA. – page 7
Electrons move from the − to the + terminal in the wire, but the (conventional) current is taken from + to −. A clamp ammeter measures large currents without being connected into the circuit. – page 7
The brain, nerves and heart work with electric signals; the sinus node sets the heartbeat. The electric eel can produce about 600 V to catch its prey. – page 7
Resistance opposes the flow of current. Ohm’s law: at constant temperature the current through a conductor is directly proportional to the potential difference across it. Georg Simon Ohm, 1789–1854. – page 8
Unit V/A = ohm (Ω); 1 kΩ = 103 Ω, 1 MΩ = 106 Ω. Resistance is caused by collisions of free electrons with the atoms of the conductor. – page 8
A resistor puts a definite resistance into a circuit (colour codes show its value). A multimeter measures resistance, potential difference and current. – page 9
Material, length (longer → more), area of cross-section (thicker → less) and temperature. Nichrome high, copper low, silver lowest. Superconductors: zero resistance at very low temperature. A rheostat changes R by changing the length of wire in the circuit. – page 9
Effective resistance = the single resistance with the same effect. In series the current is the same and V = V1 + V2. – page 10
Same potential difference; currents add I = I1 + I2; n equal resistors: R/n. The effective resistance decreases. – page 10
A battery gives current in one direction – direct current. The household supply changes direction at regular intervals – alternating current – at a high voltage, 230 V. Never do these experiments with household electricity. – page 10
3. Formulas, units & symbols
📐 Formulas & units card
series: R = R1 + R2, same I, V = V1 + V2 · parallel: 1/R = 1/R1 + 1/R2, same V, I = I1 + I2
| Quantity | Symbol | Formula | SI unit | Measured with |
|---|---|---|---|---|
| Charge വൈദ്യുതചാർജ് | Q | Q = I × t | coulomb (C) | – |
| Potential difference പൊട്ടൻഷ്യൽ വ്യത്യാസം | V | V = W ÷ Q | volt (V) = J/C | voltmeter, in parallel |
| Current വൈദ്യുതപ്രവാഹതീവ്രത | I | I = Q ÷ t | ampere (A) = C/s | ammeter, in series |
| Resistance പ്രതിരോധം | R | R = V ÷ I | ohm (Ω) = V/A | multimeter (power off) |
| Work / energy | W | W = V × Q | joule (J) | – |
| Rule | Remember |
|---|---|
| Cells | series: emfs add (n × e) · identical cells in parallel: emf of one cell, lasts longer · + to +: they cancel |
| Resistors | n equal in series: nR · n equal in parallel: R/n · two in parallel: product ÷ sum · parallel R is less than the smallest |
| Series circuit | the bigger resistor takes the bigger share of V (V ∝ R) · one break stops everything |
| Wire | R ∝ length · R ∝ 1/area · depends on material and temperature · stretched to 2× length → 4× R |
| Prefixes | 1 A = 1000 mA · 1 mA = 1000 µA · 1 kΩ = 1000 Ω · 1 MΩ = 1000 kΩ = 106 Ω · 1 min = 60 s |
| Before substituting | mA → A (÷ 1000) · kΩ → Ω (× 1000) · minutes → seconds (× 60) |
| Graph | V–I graph of a resistor: a straight line through the origin; slope = R |
🔣 Circuit symbols (Table 7.5)
| Component | Symbol | What to remember |
|---|
- Connecting a voltmeter in series or an ammeter in parallel, or ignoring the + and − terminals. Voltmeter across, ammeter in the loop, + towards the + of the cell.
- Thinking current is “used up” in a series circuit. The same current flows through every part; it is the potential difference that is shared.
- Adding resistances in parallel. Use 1/R = 1/R1 + 1/R2: 6 Ω ∥ 3 Ω = 2 Ω, less than the smallest.
- Forgetting to convert mA → A or kΩ → Ω. 20 mA = 0.02 A; 2 kΩ = 2000 Ω.
- Mixing up electron flow (− to +) with conventional current (+ to −).
- Saying the emf of cells in parallel adds up. Identical cells in parallel give the emf of one cell.
- Writing the unit of resistance as “Ω/A”, or using R = V/I with V not in volts and I not in amperes. Ω = V/A.
- Experimenting with household (mains) electricity – never.
4. Flashcards
Click a card to flip it.
5. Scored quiz
Answer all eighteen, then press Check my answers. Each wrong answer shows the page to revise. For number answers type only the number.
6. Your study checklist
Ticks come from “Mark this page as completed” at the bottom of each page.
Next: the model test paper ▶ – attempt it on paper with a timer first, then check with the solved paper.