Charge, current, voltage and resistance

Học bằng cách chơi

Trả lời những câu hỏi này để kiếm năng lượng, rồi câu cá và khám phá. Không cần tài khoản.

Dành cho nhà giáo dục: slide bài học, ghi chú ôn tập sẵn dùng cho Charge, current, voltage and resistance (MYP Physics, Year 3) — dùng trong bài giảng của bạn, hoặc chạy chủ đề như một hoạt động lớp học tương tác để người học chơi như một trò chơi trực tiếp.

Ghi chú bài học

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.

Slide

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

ĐĂNG KÝ — MIỄN PHÍ ĐĂNG NHẬP

Câu hỏi luyện tập

Xem trước miễn phí — 8 trên 52 câu hỏi. Đăng ký để xem tất cả.

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

Thêm câu hỏi

9.With the switch closed, 0.8 A flows through the first lamp. What current flows through the second lamp?
Medium
- A0 A
- B0.4 A
- C0.8 A
- D1.6 A
10.A wire of length L and cross-sectional area A has resistance R. What is the resistance of a wire of the same material with length 2L and cross-sectional area 3A?
Medium
- A(2/3)R
- B(3/2)R
- C6R
- D(1/6)R
11.A student charges a polythene rod by rubbing it with a cloth. The rod becomes negatively charged. Which statement explains how the rod becomes negatively charged?
Easy
- AThe rod gains electrons from the cloth.
- BThe rod loses electrons to the cloth.
- CThe rod gains protons from the cloth.
- DThe rod loses protons to the cloth.
12.The current in a lamp is 0.20 A and the potential difference across it is 6.0 V. What is the resistance of the lamp?
Easy
- A1.2 Ω
- B30 Ω
- C0.033 Ω
- D6.2 Ω
13.What is the unit of electric charge?
Easy
- AAmpere
- BCoulomb
- CVolt
- DOhm
14.A positively charged rod is brought near a suspended, charged balloon. The balloon is repelled. What is the charge on the balloon?
Easy
- APositive
- BNegative
- CNeutral
- DCannot be determined
15.What is the correct definition of electric current?
Easy
- AThe rate of flow of charge
- BThe energy transferred per unit charge
- CThe opposition to the flow of charge
- DThe force on a charged particle
16.Which component is used to measure potential difference?
Easy
- AAmmeter
- BVoltmeter
- COhmmeter
- DGalvanometer
17.A student uses a gold-leaf electroscope to test different materials. The electroscope is charged and the leaf rises. When a metal rod is touched to the plate, the leaf falls quickly. Which conclusion is correct?
Medium
- AMetal is a good conductor of electricity.
- BMetal is a good insulator of electricity.
- CMetal has no effect on the electroscope.
- DMetal causes the electroscope to gain more charge.
18.Which of the following is the correct definition of electric current?
Easy
- AThe rate of flow of electric charge
- BThe energy transferred per unit charge
- CThe opposition to the flow of charge
- DThe force that drives charge around a circuit
19.In an experiment to investigate how the resistance of a wire depends on its length, a student measures the potential difference across different lengths of the same wire while keeping the current constant. Which graph best shows the expected relationship between resistance R and length L?
Medium
- AA straight line through the origin with positive slope
- BA curve that flattens as L increases
- CA straight line with negative slope
- DA horizontal line
20.A student uses a gold-leaf electroscope to test whether a material is a conductor or an insulator. The electroscope is charged so that the leaf rises. When the material is touched to the plate, the leaf falls quickly. What does this indicate about the material?
Easy
- AIt is a good conductor.
- BIt is a good insulator.
- CIt is positively charged.
- DIt is negatively charged.
21.A student connects a variable resistor in series with a cell and a fixed resistor. The student measures the current and the potential difference across the fixed resistor. The variable resistor is adjusted to change the current. Which statement about the resistance of the fixed resistor is correct?
Medium
- AIt remains constant because the fixed resistor is ohmic.
- BIt increases as the current increases.
- CIt decreases as the current increases.
- DIt changes in proportion to the potential difference.
22.A student sets up a circuit with a cell, a switch, a lamp, and an ammeter in series. The ammeter reads 0.5 A. The student then adds a second identical lamp in series. What is the new reading on the ammeter?
Medium
- A0.25 A
- B0.5 A
- C1.0 A
- D0 A
23.In an experiment to measure the resistance of a wire, a student uses a circuit with a cell, an ammeter in series, and a voltmeter connected across the wire. The student records the following readings: current = 0.20 A, potential difference = 4.0 V. What is the resistance of the wire?
Easy
- A20 Ω
- B0.8 Ω
- C4.2 Ω
- D3.8 Ω
24.Which of the following is the correct way to connect a voltmeter to measure the potential difference across a lamp?
Easy
- AIn parallel with the lamp
- BIn series with the lamp
- CIn series with the cell
- DIn parallel with the ammeter
25.A student charges a gold-leaf electroscope by touching it with a negatively charged polythene rod. The leaf rises and stays risen. The student then brings a positively charged acetate rod close to the plate without touching it. What happens to the leaf?
Medium
- AIt rises further.
- BIt falls slightly.
- CIt stays at the same height.
- DIt falls completely.
26.A wire of length L and cross-sectional area A has resistance R. A second wire of the same material has length 2L and cross-sectional area A/2. What is the resistance of the second wire?
Medium
- A4R
- B2R
- CR
- DR/2
27.A student uses a circuit with a cell, a switch, a variable resistor, and a lamp in series. The student adjusts the variable resistor to increase the current. What happens to the brightness of the lamp and the potential difference across it?
Medium
- AThe lamp gets brighter and the potential difference increases.
- BThe lamp gets dimmer and the potential difference decreases.
- CThe lamp gets brighter and the potential difference decreases.
- DThe lamp gets dimmer and the potential difference increases.
28.The two lamps in series draw 1.5 A from a 12 V battery. At this current, the left-hand lamp has resistance 6 ohms. What is the resistance of the right-hand lamp?
Medium
- A2 ohms
- B8 ohms
- C4 ohms
- D6 ohms
29.A student rubs a plastic rod with a cloth. The rod becomes positively charged. Which statement explains this?
Easy
- AElectrons move from the rod to the cloth.
- BElectrons move from the cloth to the rod.
- CProtons move from the rod to the cloth.
- DProtons move from the cloth to the rod.
30.A copper wire carries a steady current. Which statement explains why charge does not build up at one point in the wire?
Easy
- ACharge enters and leaves that region at the same rate
- BProtons leave the nuclei to replace electrons
- CElectrons are used up in the wire
- DThe metal ions move out of the wire
31.Complete the sentence:
Easy
The unit of electric current is the ____.
32.A current of 0.5 A flows through a lamp for 2 minutes. Calculate the charge that flows through the lamp.
Easy
33.A current of 2.5 A flows through a lamp for 1 minute. Calculate the charge that flows through the lamp.
Easy
34.Complete the sentence using the words provided:
Medium
When a polythene rod is rubbed with a cloth, electrons are transferred from the ____ to the ____. The cloth becomes ____ charged and the rod becomes ____ charged.
35.Like charges attract each other.
Easy
True or false?
36.Which of the following is a correct definition of potential difference?
Medium
- AThe rate of flow of electric charge
- BThe work done by a unit charge passing through a component
- CThe opposition to current
- DThe electrical work done by a source in moving a unit charge around a complete circuit
37.A voltmeter should be connected in series with the component being measured.
Easy
True or false?
38.A wire of length L and cross-sectional area A has resistance R. What is the resistance of a wire of the same material with length 2L and cross-sectional area 2A?
Medium
- AR
- B2R
- CR/2
- D4R
39.Which of the following materials is a good insulator?
Easy
- ASilver
- BCopper
- CRubber
- DAluminium
40.Match each component to its correct circuit symbol.
Medium
- Cell
- Lamp
- Resistor
- Ammeter
- A circle with a cross inside
- A rectangle
- Two parallel lines (long and short)
- A circle with an 'A' inside
41.Measure current through a resistor at several low voltages in a teacher-approved circuit. What is the independent variable?
Easy
- Acurrent in amperes
- Bthe number of repeated trials
- Cthe potential difference across the resistor
- Dthe scientific explanation written afterwards
42.Measure current through a resistor at several low voltages in a teacher-approved circuit. Which observation or quantity is the dependent variable?
Easy
- Athe potential difference across the resistor
- Bthe title given to the investigation
- Cthe number of references in the report
- Dcurrent in amperes
43.Measure current through a resistor at several low voltages in a teacher-approved circuit. Which decision best controls another factor in this comparison?
Medium
- Akeep the resistor's temperature approximately constant
- Bchange every condition for each trial
- Cuse a different measurement method for every result
- Drecord only results that agree with the prediction
44.Measure current through a resistor at several low voltages in a teacher-approved circuit. Why should the class repeat measurements or check multiple comparable observations?
Medium
- ATo guarantee that every systematic error disappears
- BTo assess variation and judge how consistent the evidence is
- CTo make an unsupported prediction become correct
- DTo avoid reporting results that disagree with a model
45.A class is evaluating an application of charge, current, voltage and resistance. Which statement identifies a relevant limitation?
Hard
- AAll scientific models reproduce every feature of the real world
- BOne favourable result proves that a technology has no disadvantages
- CA resistor that heats up may change resistance, so constant resistance must be tested rather than assumed.
- DA conclusion needs no evidence when a scientific term is used
46.Measure current through a resistor at several low voltages in a teacher-approved circuit. Which conclusion is most justified by a controlled comparison?
Hard
- AA claim that the result must hold in all possible conditions
- BA claim that alternative explanations never need testing
- CA claim based only on the most convenient observation
- DA conclusion restricted to the tested conditions, with uncertainty and limitations stated
47.Measure current through a resistor at several low voltages in a teacher-approved circuit. Select the two practices that strengthen the validity of this comparison.
Medium
- Akeep the resistor's temperature approximately constant
- Bchange the measurement method whenever a result is unexpected
- Crecord current in amperes using the same agreed procedure
- Dreport only observations that confirm the prediction
48.When evaluating evidence about charge, current, voltage and resistance, select the two scientifically defensible statements.
Hard
- AOne result proves the explanation in every situation
- BA resistor that heats up may change resistance, so constant resistance must be tested rather than assumed.
- CA conclusion should state the conditions and uncertainty of the evidence
- DModels never need revision when new evidence appears
49.Design a fair investigation for this question: Measure current through a resistor at several low voltages in a teacher-approved circuit. Identify what to compare, what to record and one control.
Medium
50.Explain one use of the science in charge, current, voltage and resistance and evaluate one limitation of the evidence or application.
Hard
51.A resistor has 6.0 V across it and carries 0.30 A. What is its resistance?
Hard
- A20 ohms
- B1.8 ohms
- C0.050 ohms
- D6.3 ohms
52.A class doubles the voltage across a resistor but the current less than doubles as it warms. Which explanation is consistent?
Hard
- AThe resistor must have lost every electron
- BThe resistance increased as temperature rose
- CCurrent has stopped carrying charge
- DThe resistance is necessarily constant under all conditions

Ghi chú ôn tập

## 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)**. ## 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. ## 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. ## 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: \( P = I^2R \) and \( P = \frac{V^2}{R} \). ## 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.

Electric Fields: An **electric field** is a region where a charge experiences a force.
Conductors and Insulators: **Conductors** (e.g., metals) allow charge to flow easily because they have **delocalised electrons**.
Electric Current: Define electric current as rate of flow of charge and measure it with an ammeter.
Electric Charge Interactions: Understand positive and negative charges, attraction and repulsion, and charging by friction.
Designing scientific inquiries: Plan a fair comparison: Measure current through a resistor at several low voltages in a teacher-approved circuit.
Evaluating evidence and impacts: 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.
Electric Charge: There are two types of electric charge: **positive** and **negative**.
Charging by Friction: Rubbing two insulating materials together transfers **electrons** from one to the other.
Current: **Electric current** is the **rate of flow of charge**.
Direct and Alternating Current: **Direct current (d.c.)** flows in **one direction** only; produced by cells and batteries.
Electromotive Force and Potential Difference: **Electromotive force (e.m.f.)** is the energy supplied per unit charge by a source: \( E = \frac{W}{Q} \).
Resistance and Ohm's Law: **Resistance** is the opposition to current; measured in **ohms (Ω)**.
Resistance of a Wire: Resistance is **directly proportional** to length: longer wire → higher resistance.
Electrical Energy and Power: **Electrical power** \( P = VI \), measured in **watts (W)**.
positive: **Conventional current** flows from **positive** to **negative** terminal (opposite to electron flow).
negative: **Conventional current** flows from **positive** to **negative** terminal (opposite to electron flow).

Thẻ ghi nhớ

A polythene rod is rubbed with a cloth and becomes negatively charged. This happens because

electrons move from the cloth to the rod When a polythene rod is rubbed with a cloth, electrons are transferred from the cloth to the rod, giving the rod a negative charge. Protons do not move in charging by friction.

Which of the following is a good conductor of electricity?

Copper Copper is a metal and a good conductor of electricity. Rubber, plastic, and glass are insulators.

A lamp is rated at 12 V, 50 W. What is the current through the lamp when operating normally?

4.17 A Power = voltage × current, so current = power / voltage = 50 W / 12 V = 4.17 A. Option A results from multiplying instead of dividing, C from 12×50, D from 50/1.3.

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?

5 V Using Ohm's law V = IR = 0.5 A × 10 Ω = 5 V. Option A is I/R, C is R/I, D is sum.

A student connects a voltmeter to measure the potential difference across a lamp. How should the voltmeter be connected?

In parallel with the lamp A voltmeter must be connected in parallel with the component across which the potential difference is to be measured. Series connection is for ammeters.

A charge of 270 kC passes through a 12 V battery. How much electrical energy is transferred?

3.24 × 10⁶ J Energy = charge × voltage = 270,000 C × 12 V = 3,240,000 J = 3.24 × 10⁶ J. Option A is charge/voltage, C is misplacing decimal, D is 270×12×10^?

Two identical resistors are connected in parallel. The total resistance is 2 Ω. What is the resistance of each resistor?

4 Ω For two identical resistors in parallel, total resistance R_total = R/2, so R = 2 × R_total = 4 Ω. Option A is half of total, B is same as total, D is quarter.

What is the unit of electromotive force (e.m.f.)?

Volt E.m.f. is measured in volts (V). Ampere is for current, ohm for resistance, coulomb for charge.

With the switch closed, 0.8 A flows through the first lamp. What current flows through the second lamp?

0.8 A There is one path for current, so both lamps carry 0.8 A.

A wire of length L and cross-sectional area A has resistance R. What is the resistance of a wire of the same material with length 2L and cross-sectional area 3A?

(2/3)R Resistance is proportional to length and inversely proportional to area. New resistance = (2L/ L) × (A/3A) × R = 2/3 R. Option B reverses ratio, C multiplies both, D inverts.

A student charges a polythene rod by rubbing it with a cloth. The rod becomes negatively charged. Which statement explains how the rod becomes negatively charged?

The rod gains electrons from the cloth. When rubbed, electrons transfer from the cloth to the rod, giving the rod a negative charge. Protons are not free to move.

The current in a lamp is 0.20 A and the potential difference across it is 6.0 V. What is the resistance of the lamp?

30 Ω Using Ohm's law, R = V/I = 6.0 V / 0.20 A = 30 Ω.

What is the unit of electric charge?

Coulomb Electric charge is measured in coulombs (C). Ampere is for current, volt for potential difference, ohm for resistance.

A positively charged rod is brought near a suspended, charged balloon. The balloon is repelled. What is the charge on the balloon?

Positive Like charges repel. Since the rod is positive, the balloon must also be positive to be repelled.

What is the correct definition of electric current?

The rate of flow of charge Current is defined as the rate of flow of electric charge, measured in amperes.

Which component is used to measure potential difference?

Voltmeter A voltmeter measures potential difference (voltage) and is connected in parallel.

How would you design the inquiry for charge, current, voltage and resistance?

Measure current through a resistor at several low voltages in a teacher-approved circuit. Compare the potential difference across the resistor; record current in amperes; keep the resistor's temperature approximately constant.

What limitation matters when applying charge, current, voltage and resistance?

A resistor that heats up may change resistance, so constant resistance must be tested rather than assumed.

Unlock all 52 questions, flashcards & more

Tạo tài khoản miễn phí để xem mọi câu hỏi, slide, thẻ ghi nhớ và ghi chú ôn tập cho chủ đề này.

ĐĂNG KÝ — MIỄN PHÍ ĐĂNG NHẬP

Đề thi cũ

Luyện đề thi cũ cho chủ đề này sắp ra mắt.

Sắp ra mắt