Transcript 7J Circuits - Science-Magic-for-OBK-Prep-7th

7J Electrical circuits
7J
Electrical circuits
Connecting circuits
Circuits and current
Circuits and energy
Circuits summary
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7J Electrical circuits
Connecting circuits
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7J Connecting circuits – Making electrical objects work
All electrical objects need 3 things to make them work.
What are they?
1. A power supply
- like a cell (battery)
or a mains supply.
2. Wires
- provide a path for electrical
charge to pass through.
3. An electrical device
- like a bulb or a motor.
What must happen for the electrical device to work?
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7J Connecting circuits – A simple circuit
An electrical device only works when all the components
are connected to make a complete circuit.
When the switch is turned on, the circuit is complete.
What happens to the bulb?
Electrical charge flows around a complete circuit.
The flow of electrical charge is called the current.
What happens to the current if there is a gap in the circuit
or the switch is turned off?
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7J Connecting circuits – Electrical symbols
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7J Connecting circuits – Match the symbol
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7J Connecting circuits – Switch on
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7J Connecting circuits – Circuits quiz
1. The parts that are connected to make an electrical
circuit are called…
a) computers.
b) components.
c) consonants.
2. The three things needed to make a circuit are
a power supply, an electrical device and…
a) wires.
b) a plug.
c) batteries.
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7J Connecting circuits – Circuits quiz
3. The flow of electrical charge around a circuit is called the…
a) raisin.
b) battery.
c) current.
4. The symbol
component?
represents which electrical
a) A switch.
b) A bulb.
c) An ammeter.
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7J Connecting circuits – Circuits quiz
5. What is the symbol for a cell?
a)
b)
c)
6. When a switch is closed, an electrical circuit is said to be…
a) complete.
b) broken.
c) positive.
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7J Connecting circuits – Circuits quiz
7. Batteries should be connected so that their poles are
arranged…
a) positive to positive.
b) negative to negative.
c) positive to negative.
8. When a circuit is broken, what happens to the current?
a) the current continues to flow.
b) the current changes direction.
c) the current no longer flows.
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7J Electrical circuits
Circuits and current
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7J Circuits and current - What is a series circuit?
A series circuit is a continuous loop with no branches.
Match each series circuit to the correct circuit diagram.
A
B
1
3
22
C
31
What do the ammeter readings tell you about the current
in a series circuit?
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7J Circuits and current – Current in a series circuit
Is current the same in all parts of a series circuit?
3A
3A
3A
The total current leaving the cell is 3A.
The current before the lamp is 3A.
The current after the lamp and returning to the cell
is also 3A.
Is the current used up?
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7J Circuits and current - Series circuits and the water model
Water flowing in pipes helps to explain what happens in
an electrical circuit.
water
pump
valve
(open)
narrow pipe
(harder for the water to flow)
Which parts of the water model match the electrical
components?
Why is it harder for water to flow in the narrow pipe?
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7J Circuits and current - Series circuits and the water model
The narrow pipe resists the flow of water.
water
pump
valve
(open)
narrow pipe
Electrical components can resist the flow of current.
These are called resistors.
Where is there resistance in this electrical circuit?
The thin wires in a filament bulb resist the current.
How do they show resistance?
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7J Circuits and current - Resistance
Both these circuits have the same number of batteries.
D
E
Why do the ammeters show different current readings?
There is less current in circuit E which means it's harder
for the current to flow in the circuit with the motor.
Which component has the greater resistance?
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7J Circuits and current - What is a parallel circuit?
A parallel circuit contains branches with more than
one route for the current.
Route 1
junction point
Route 2
Where are the two routes in this parallel circuit?
At a junction point the current can divide between
the two routes.
Will the current be the same in all parts of a parallel
circuit?
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7J Circuits and current – Current in a parallel circuit
Is current the same in all parts of a parallel circuit?
3A
3A
1.5A
1.5A
The total current leaving the cell is 3A.
This 3A divides up so that 1.5A goes on route 1
and the other 1.5A goes on route 2.
The current returning to the cell is 3A.
Is the current used up?
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7J Circuits and current - Parallel circuits and the water model
The water model can also help to explain what happens
in a parallel circuit.
water
pump
The water valves act like switches in the circuit.
What happens to the flow of water when a valve is closed?
What happens to the current in the matching part of the
parallel circuit?
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7J Electrical circuits
Circuits and energy
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7J Circuits and energy - What do batteries do?
A battery is an energy source that stores chemical energy.
What happens to this energy in an electrical circuit?
chemical energy
in battery
What happens to the
electrical energy
in this circuit?
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electrical energy
in circuit
7J Circuits and energy - Why don't batteries last forever?
Current transfers energy to different parts of a circuit.
Electrical energy is used up and converted into
other types of energy in the circuit.
Complete these energy transformations:
motor
electrical energy
in circuit
movement energy
in motor
bulb
electrical energy
in circuit
light and heat energy
in bulb
Why don’t batteries last forever?
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7J Circuits and energy - Increasing voltage
A battery gives current a "push" around a circuit.
The amount of "push" from the battery is the voltage.
F
G
H
In which circuit does the bulb shine brightest and why?
Is the current affected by the voltage?
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7J Electrical circuits
Circuits summary
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7J Circuits summary – Build a circuit
Build a circuit
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7J Circuits summary – True or false?
True or False?
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