Charge, current, voltage and resistance
விளையாடிக் கற்றுக்கொள்ளுங்கள்
ஆற்றல் சம்பாதிக்க இந்த கேள்விகளுக்குப் பதிலளியுங்கள், பின்னர் மீன் பிடித்து ஆராயுங்கள். கணக்கு தேவையில்லை.
கல்வியாளர்களுக்கு: Charge, current, voltage and resistance (MYP Physics, Year 3)-க்கான தயாரான பாட ஸ்லைடுகள், திருப்புதல் குறிப்புகள் — உங்கள் பாடத்தில் அவற்றைப் பயன்படுத்தவும், அல்லது கற்பவர்கள் நேரலை விளையாட்டாக விளையாடும் ஊடாடும் வகுப்பு செயல்பாடாக தலைப்பை இயக்கவும்.
பாட குறிப்புகள்
Big idea: charge, current, voltage and resistance
- Key concept: Relationships. Current is charge flow per unit time. Potential difference is energy transferred per unit charge; resistance equals potential difference divided by current.
- Related concepts: Models and evidence. Use a scientific explanation to make predictions, then test it against observations.
- Global context: Scientific and technical innovation. Electrical relationships help choose components for low-voltage devices.
Electric Charge
- There are two types of electric charge: positive and negative.
- Inside an atom, electrons are negatively charged, protons are positively charged, and neutrons are neutral.
- Atoms have equal numbers of protons and electrons, so overall they are neutral.
- Like charges repel, opposite charges attract.
- Electric charge is measured in coulombs (C).
Structure of an atom showing protons, neutrons and electron shells.
Charging by Friction
- Rubbing two insulating materials together transfers electrons from one to the other.
- The material that gains electrons becomes negatively charged; the material that loses electrons becomes positively charged.
- Example: rubbing a polythene rod with a cloth transfers electrons from the cloth to the rod → rod becomes negative, cloth becomes positive.
- Example: rubbing an acetate rod with a cloth transfers electrons from the rod to the cloth → rod becomes positive, cloth becomes negative.
- Only electrons move during charging by friction; protons do not move.
Apparatus for demonstrating charging by friction using a polythene rod and another insulating material.
Electric Fields
- An electric field is a region where a charge experiences a force.
- Field lines are directed from positive to negative charge.
- Around a point charge, field lines are radial: outward for positive, inward for negative.
- Between two parallel plates, the field is uniform with parallel, equally spaced lines.
- Field lines are always perpendicular to the surface of a conductor.
Demonstration of a Van de Graaff generator with streamers and field lines around a charged sphere.
Conductors and Insulators
- Conductors (e.g., metals) allow charge to flow easily because they have delocalised electrons.
- Insulators (e.g., plastic, rubber, glass) have no free charges and do not allow charge to flow easily.
- A gold-leaf electroscope can test conductivity: a good conductor makes the leaf fall quickly; an insulator makes it fall slowly or not at all.
Current
- Electric current is the rate of flow of charge.
- Current is measured in amperes (A) using an ammeter connected in series.
- Conventional current flows from positive to negative terminal (opposite to electron flow).
- Equation: I = \frac{Q}{t} , where Q is charge in coulombs, t is time in seconds.
- In metals, current is a flow of negatively charged electrons.
Direct and Alternating Current
- Direct current (d.c.) flows in one direction only; produced by cells and batteries.
- Alternating current (a.c.) changes direction periodically; produced by mains electricity (UK: 230 V, 50 Hz).
- Graph of d.c. is a horizontal line; graph of a.c. is a sine wave.
Electromotive Force and Potential Difference
- Electromotive force (e.m.f.) is the energy supplied per unit charge by a source: E = \frac{W}{Q} .
- Potential difference (p.d.) is the energy transferred per unit charge across a component: V = \frac{W}{Q} .
- Both are measured in volts (V).
- Voltmeter is connected in parallel to measure p.d.
Resistance and Ohm's Law
- Resistance is the opposition to current; measured in ohms (Ω).
- Ohm's law: R = \frac{V}{I} .
- For a fixed resistor at constant temperature, current is directly proportional to voltage (ohmic conductor).
- For a filament lamp, resistance increases with temperature (non-ohmic).
- A diode allows current in one direction only (forward bias).
Resistance of a Wire
- Resistance is directly proportional to length: longer wire → higher resistance.
- Resistance is inversely proportional to cross-sectional area: thicker wire → lower resistance.
- Increasing temperature increases resistance due to more frequent collisions with vibrating metal ions.
Electrical Energy and Power
- Electrical power P = VI , measured in watts (W).
- Electrical energy E = VIt , measured in joules (J).
- Alternative: P = I2R and P = \frac{V2}{R} .
Think like a scientist
- Measure current through a resistor at several low voltages in a teacher-approved circuit.
- Comparison: the potential difference across the resistor. Outcome: current in amperes.
- Control: keep the resistor's temperature approximately constant. Explain why this makes the comparison fairer.
- Evidence: Use a consistent method, repeated observations where appropriate and a table with labelled quantities and units. Keep unexpected results and investigate their cause.
- Safety: Practical activities need teacher supervision and an appropriate risk assessment. Use the provided data or simulation where the investigation specifies it.
- Inquiry task: State a testable question, predict the outcome using the science, then explain how your observations would support or challenge the prediction.
Evaluate the science
- Electrical relationships help choose components for low-voltage devices.
- A resistor that heats up may change resistance, so constant resistance must be tested rather than assumed.
- Evaluation task: Link your conclusion to evidence, identify a limitation and suggest a specific improvement. Distinguish a measured result from an explanation of its cause.
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பயிற்சி கேள்விகள்
இலவச முன்னோட்டம் — 52-இல் 8 கேள்விகள். அனைத்தையும் பார்க்க பதிவு செய்யவும்.
1.A polythene rod is rubbed with a cloth and becomes negatively charged. This happens because
Easy- Aelectrons move from the cloth to the rod
- Belectrons move from the rod to the cloth
- Cprotons move from the cloth to the rod
- Dprotons move from the rod to the cloth
2.Which of the following is a good conductor of electricity?
Easy- ARubber
- BPlastic
- CCopper
- DGlass
3.A lamp is rated at 12 V, 50 W. What is the current through the lamp when operating normally?
Medium- A0.24 A
- B4.17 A
- C600 A
- D38 A
4.The resistance of a wire is 10 Ω. What is the potential difference across the wire when a current of 0.5 A flows through it?
Easy- A0.05 V
- B5 V
- C20 V
- D10.5 V
5.A student connects a voltmeter to measure the potential difference across a lamp. How should the voltmeter be connected?
Easy- AIn series with the lamp
- BIn parallel with the lamp
- CIn series with the power supply
- DIn parallel with the power supply
6.A charge of 270 kC passes through a 12 V battery. How much electrical energy is transferred?
Medium- A22.5 J
- B3.24 × 106 J
- C3.24 × 103 J
- D2.25 × 104 J
7.Two identical resistors are connected in parallel. The total resistance is 2 Ω. What is the resistance of each resistor?
Medium- A1 Ω
- B2 Ω
- C4 Ω
- D0.5 Ω
8.What is the unit of electromotive force (e.m.f.)?
Easy- AAmpere
- BVolt
- COhm
- DCoulomb
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இந்த தலைப்பிற்கான ஒவ்வொரு கேள்வியையும், ஸ்லைடுகளையும், ஃப்ளாஷ் கார்டுகளையும் மற்றும் திருப்புதல் குறிப்புகளையும் பார்க்க இலவச கணக்கை உருவாக்கவும்.
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இந்த தலைப்பிற்கான முந்தைய தேர்வு பயிற்சி விரைவில் வருகிறது.
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