Current

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課程筆記

What is Current?

Current is the flow of charge through a circuit.
It is equal to how much charge flows past a point every second.
The charged particles that flow are electrons (negatively charged).
A complete circuit is needed for current to flow.

Measuring Current

Current is measured in amps (A).
An ammeter measures current at a point in the circuit.
The circuit symbol for an ammeter is a circle with an “A” inside.

Series Circuits

A series circuit has only one path for current.
Current is the same everywhere in a series circuit.
Example: a series circuit with one lamp has 2 A at every point.

Parallel Circuits

A parallel circuit has more than one path for current.
At a junction, total current in equals total current out.
Each branch draws current from the cell; total current is the sum of branch currents.
Higher resistance in a path means lower current in that path.

Current and Resistance

Resistance opposes current flow.
In a parallel circuit with identical lamps, each branch has the same current.
If one path has more lamps (more resistance), its current is less.
Overall current from the battery is the sum of the branch currents.

A series circuit with a cell, switch, lamp, and ammeter. Current is the same at all points.

In a series circuit, the ammeter readings are equal (2 A everywhere).

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練習題

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1.What is the unit of electric current?
Easy
- AAmps
- BVolts
- COhms
- DWatts
2.Which instrument is used to measure electric current?
Easy
- AVoltmeter
- BAmmeter
- COhmmeter
- DGalvanometer
3.What particles flow through a circuit to create an electric current?
Easy
- AProtons
- BNeutrons
- CElectrons
- DIons
4.In a series circuit, the current is:
Easy
- Adifferent at different points
- Bthe same everywhere
- Chigher near the battery
- Dlower near the bulb
5.In a parallel circuit, the total current entering a junction is equal to:
Easy
- Athe current in the smallest branch
- Bthe average of the branch currents
- Cthe total current leaving the junction
- Dthe current in the largest branch
6.A series circuit has a 2 A current. What is the current after passing through a lamp?
Easy
- A0 A
- B1 A
- C2 A
- D4 A
7.In a parallel circuit with two identical lamps, the current in each branch is 2 A. What is the total current drawn from the battery?
Easy
- A2 A
- B4 A
- C1 A
- D0 A
8.In a parallel circuit, one branch has a single lamp and the other branch has two identical lamps in series. The current through the single lamp is 2 A. What is the current through each of the two lamps?
Medium
- A2 A each
- B1 A each
- C0.5 A each
- D4 A each

更多題目

9.A parallel circuit has three identical lamps in separate branches. The total current from the battery is 6 A. What is the current in each lamp?
Easy
- A2 A
- B3 A
- C6 A
- D1 A
10.Which of these is the correct circuit symbol for an ammeter?
Easy
- AA circle with an A inside
- BA circle with a V inside
- CA zigzag line
- DA straight line with a dot
11.Current can only flow if the circuit is:
Easy
- Acomplete
- Bbroken
- Copen
- Dswitched off
12.In the circuit shown, what is the current at point X?
Easy
- A2 A
- B4 A
- C1 A
- D0 A
13.In a parallel circuit with two branches, one branch has a 2 A current and the other branch has a 1 A current. What is the total current drawn from the battery?
Easy
- A3 A
- B2 A
- C1 A
- D1.5 A
14.A series circuit contains a cell, a switch, a lamp, and an ammeter. The ammeter reads 0.5 A. If another identical lamp is added in series, what will the new ammeter reading be?
Medium
- A0.25 A
- B0.5 A
- C1.0 A
- D0.75 A
15.The diagram shows a series circuit with a cell and two lamps. The current at point X is 0.3 A. What is the current at point Y?
Easy
- A0.3 A
- B0.15 A
- C0.6 A
- D0 A
16.In a parallel circuit with two identical lamps, the current through each lamp is 1.5 A. What is the total current from the battery?
Easy
- A3.0 A
- B1.5 A
- C0.75 A
- D2.0 A
17.A circuit has a cell and two identical lamps connected in parallel. One lamp is removed. What happens to the current through the remaining lamp?
Medium
- AIt stays the same
- BIt halves
- CIt doubles
- DIt becomes zero
18.Which of the following is the correct definition of electric current?
Easy
- AThe amount of charge flowing past a point per second
- BThe energy carried by electrons
- CThe number of electrons in a wire
- DThe voltage across a component
19.A student sets up the circuit shown. The ammeter reads 2 A. What is the current through lamp L1?
Easy
- A2 A
- B1 A
- C0.5 A
- D4 A
20.In a parallel circuit, the total current entering a junction is 5 A. One branch has a current of 2 A. What is the current in the other branch?
Easy
- A3 A
- B5 A
- C2 A
- D7 A
21.A circuit has three identical lamps in parallel. The total current from the battery is 6 A. If one lamp is removed, what is the new total current?
Medium
- A4 A
- B6 A
- C2 A
- D3 A
22.Which of the following statements about current in a series circuit is correct?
Easy
- ACurrent is the same at all points
- BCurrent is different at different points
- CCurrent increases after passing through a bulb
- DCurrent decreases after passing through a bulb
23.A student connects an ammeter in a circuit. The ammeter reads 0.8 A. Which of the following could cause the reading to increase?
Medium
- AAdding another bulb in series
- BRemoving a bulb from a parallel branch
- CIncreasing the number of cells
- DOpening the switch
24.A student sets up a series circuit with a cell, an ammeter, and a lamp. The ammeter reads 0.5 A. The student then adds a second identical lamp in series. What will the new ammeter reading be?
Medium
- A0.25 A
- B0.5 A
- C1.0 A
- D0.0 A
25.In the circuit shown, the ammeter reads 2 A. What is the current through the lamp?
Easy
- A0 A
- B1 A
- C2 A
- D4 A
26.A parallel circuit has two branches. Branch A has one lamp, branch B has two identical lamps in series. The current in branch A is 2 A. What is the total current from the battery?
Medium
- A2 A
- B3 A
- C4 A
- D6 A
27.Which of the following is the correct circuit symbol for an ammeter?
Easy
- AA circle with an 'A' inside
- BA circle with a 'V' inside
- CA rectangle with an 'A' inside
- DA triangle with an 'A' inside
28.In a parallel circuit with three identical lamps in separate branches, the total current from the battery is 6 A. If one lamp is removed, what is the new total current?
Medium
- A2 A
- B4 A
- C6 A
- D3 A
29.A student connects a circuit with a cell, a switch, a lamp, and an ammeter. The ammeter reads 0.5 A. The student then opens the switch. What will the ammeter read?
Easy
- A0.5 A
- B0 A
- CInfinite
- D0.25 A
30.Which of the following statements about current in a parallel circuit is correct?
Easy
- AThe current is the same in all branches.
- BThe total current entering a junction equals the total current leaving the junction.
- CThe current is the same everywhere in the circuit.
- DThe current is smaller in branches with lower resistance.
31.A series circuit contains a 3 V battery and two identical lamps. The current measured is 0.2 A. What is the current if a third identical lamp is added in series?
Medium
- A0.2 A
- B0.1 A
- C0.3 A
- D0.067 A
32.A student wants to measure the current through a lamp. How should the ammeter be connected?
Easy
- AIn series with the lamp
- BIn parallel with the lamp
- CAcross the battery terminals
- DNext to the switch
33.What particles flow through a metal wire to create an electric current?
Easy
- AProtons
- BNeutrons
- CElectrons
- DIons
34.In the circuit shown, the ammeter reads 4 A. What is the current at point X?
Medium
- A1 A
- B2 A
- C3 A
- D4 A
35.In a parallel circuit, one branch has a single lamp and the other branch has two identical lamps in series. The current through the single lamp is 2 A. What is the current through each lamp in the two-lamp branch?
Medium
- A1 A
- B2 A
- C0.5 A
- D4 A
36.A student sets up a series circuit with a cell, a switch, and a lamp. The ammeter reads 0.5 A. The student then adds a second identical lamp in series. What will the new ammeter reading be?
Medium
- A0.25 A
- B0.5 A
- C1.0 A
- D0.0 A
37.In the circuit shown, the ammeter reads 2 A. What is the current through lamp L1?
Easy
- A2 A
- B1 A
- C4 A
- D0 A
38.A parallel circuit has two branches. Branch A has one lamp, branch B has two identical lamps in series. The current in branch A is 2 A. What is the total current drawn from the battery?
Medium
- A2 A
- B3 A
- C4 A
- D6 A
39.A parallel circuit has three identical lamps in separate branches. The total current from the battery is 6 A. If one lamp is removed, what is the new total current?
Medium
- A6 A
- B4 A
- C2 A
- D3 A
40.A student builds a series circuit with a cell, a switch, and a lamp. She closes the switch and the lamp lights. She then adds an ammeter in series between the cell and the switch. The ammeter reads 0.5 A. She then moves the ammeter to a position between the lamp and the switch. What will the ammeter read now?
Easy
- A0.5 A
- B0 A
- C1.0 A
- D0.25 A
41.Current is equal to how much charge is flowing past a point in the circuit every second.
Easy
True or false?
42.Protons are the charged particles that flow through a circuit.
Easy
True or false?
43.Current can flow through an incomplete circuit.
Easy
True or false?
44.In a series circuit, current is different at different points.
Easy
True or false?
45.In a series circuit with a cell and two identical lamps, the current at one point is 0.5 A. What is the current through each lamp?
Easy
- A0.5 A
- B0.25 A
- C1.0 A
- D0 A
46.A parallel circuit has two identical branches. The total current from the battery is 4 A. What is the current in each branch?
Easy
- A2 A
- B4 A
- C1 A
- D8 A
47.In a parallel circuit, one branch has a single lamp and the other branch has two identical lamps in series. The current through the single lamp is 2 A. What is the total current from the battery?
Medium
- A3 A
- B2 A
- C4 A
- D6 A
48.Match each circuit component to its symbol description.
Medium
- Cell
- Lamp
- Ammeter
- Circle with an A
- Two parallel lines (long and short)
- Circle with a cross inside
49.Order the following steps to measure current through a lamp:
Easy
- Close the switch
- Connect the ammeter in series with the lamp
- Open the switch to break the circuit
- Read the current on the ammeter
50.Which of the following are true about current in a parallel circuit? (select all that apply)
Medium
- ACurrent splits at junctions
- BTotal current entering a junction equals total current leaving
- CCurrent is the same in every branch
- DAdding more branches increases total current from the battery
51.Complete the sentence:
Easy
Current is measured in units called ____.
52.A series circuit has a current of 2 A. What is the current at any point in the circuit?
Easy
53.A parallel circuit has a 6 A total current. One branch has a current of 2 A. What is the current in the other branch?
Medium
54.State what we use to measure current in a circuit.
Easy
55.A parallel circuit has three branches. Branch A has 2 A, branch B has 1.5 A, and branch C has 0.5 A. What is the total current from the battery?
Medium
56.What is the circuit symbol for a lamp?
Easy
57.A parallel circuit has two branches. One branch has a current of 3 A, the other 2 A. What is the total current from the battery?
Easy
58.Explain why adding a second identical lamp in series reduces the current in the circuit.
Hard
59.Explain why current is the same everywhere in a series circuit.
Medium
60.A student connects a circuit with a cell and two lamps in parallel. The ammeter in the main circuit reads 0.8 A. One lamp is then removed. Explain what happens to the ammeter reading.
Hard
61.A series circuit has a current of 2 A. What is the current at any point in the circuit?
Easy
- A3 A
- B1 A
- C2 A
- D4 A
62.A parallel circuit has a 6 A total current. One branch has a current of 2 A. What is the current in the other branch?
Medium
- A5 A
- B6 A
- C3 A
- D4 A
63.A parallel circuit has three branches. Branch A has 2 A, branch B has 1.5 A, and branch C has 0.5 A. What is the total current from the battery?
Medium
- A6 A
- B4 A
- C3 A
- D5 A
64.A parallel circuit has two branches. One branch has a current of 3 A, the other 2 A. What is the total current from the battery?
Easy
- A7 A
- B5 A
- C4 A
- D6 A

複習筆記

## Current in Circuits - **Current** is the flow of charge (electrons) past a point per second. Measured in **amps (A)** using an **ammeter** (symbol: circle with 'A'). - A **complete circuit** is needed for current to flow. - **Series circuit**: only one path; current is **the same everywhere**. - **Parallel circuit**: multiple paths; at a junction, **total current in = total current out**. Each branch draws additional current from the cell. - **Resistance** affects current: higher resistance → lower current. ### Key Rules - In series: \( I_{total} = I_1 = I_2 = ... \) - In parallel: \( I_{total} = I_1 + I_2 + ... \) (current splits at junctions) ### Example (from source) - Identical lamps: each branch gets same current (e.g., 2 A). Before/after junction, total current is sum (e.g., 4 A). - If one branch has more lamps (higher resistance), its current is lower (e.g., 2 A vs 1 A). Total drawn from battery = sum of branch currents (e.g., 3 A).

Current: The rate of flow of charge past a point in a circuit, measured in amps (A).
Ammeter: A device used to measure current, connected in series. Symbol: circle with 'A'.
Electron: A negatively charged particle that flows through a circuit.
Series circuit: A circuit with only one path for current; current is the same at all points.
Parallel circuit: A circuit with more than one path for current; total current into a junction equals total current out.
Junction: A point in a circuit where wires split or combine.
Resistance: A property that opposes current flow; higher resistance reduces current.

字卡

What is electric current?

Current is the flow of charge past a point in a circuit every second.

What is the unit of current?

Amps (A).

What instrument measures current?

An ammeter.

What is the circuit symbol for an ammeter?

A circle with an 'A' inside.

What charged particles flow through a circuit?

Electrons, which are negatively charged.

What is needed for current to flow?

A complete circuit.

In a series circuit, how does current compare at different points?

Current is the same everywhere in a series circuit.

How many paths for current are there in a series circuit?

Only one path.

In a parallel circuit, what is the rule for current at a junction?

The total current going into a junction equals the total current going out.

How does resistance affect current in a path?

Higher resistance leads to lower current.

In a parallel circuit with identical lamps, how does current in each branch compare?

Each branch has the same current if the lamps are identical.

If a parallel circuit has two identical branches each with 2 A, what is the total current before the junction?

4 A.

In a series circuit with one lamp, if current is 2 A at one point, what is it at another point?

2 A, because current is the same everywhere.

What happens to current when you add more lamps in series?

Current decreases because total resistance increases.

In a parallel circuit, if one branch has two lamps and another has one lamp (identical lamps), which branch has higher current?

The branch with one lamp has higher current because it has lower resistance.

True or False: Current is equal to how much charge flows past a point per second.

True.

True or False: Protons flow through a circuit.

False. Electrons flow.

True or False: Current can flow through an incomplete circuit.

False. A complete circuit is needed.

True or False: In a series circuit, current is different at different points.

False. Current is the same everywhere.

What is the circuit symbol for a cell?

Two parallel lines, one longer (positive) and one shorter (negative).

What is the circuit symbol for a lamp?

A circle with a cross inside.

In a parallel circuit with two branches, one with 2 A and one with 1 A, what is the total current from the battery?

3 A.

How does adding more lamps in parallel affect the total current drawn from the battery?

It increases because each branch adds more current.

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