Transcript N45 Electricity 2 20Q

Twenty Questions
Electricity 2
Twenty Questions
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1. Give 1 advantage of using a
circuit breaker compared with a
fuse.
• Reset instead of
replaced.
• Easier to see if it’s
off.
2. What type of appliance uses the
greatest power?
• One which produces
heat.
3. Upon what does the size of an
appliances flex depend?
• It’s power rating.
4. In a house are the mains wires in
series or parallel? Why?
• Parallel.
•So each appliance can
be switched on/off
separately.
•Each appliance will
have 230V across it.
5. A heater has a current of 6A
flowing through it for 4 minutes,
what charge will pass through it.
•Q = It
= 6 x (4 x 60)
= 1440 C
6. Draw the electrical field
surrounding a negative point charge.
7. State Ohm’s Law
• R=V÷I
8. Draw the symbol for a fuse.
• Rectangle with the
wire passing through it.
9. Give an example each of a d.c.
and an a.c. power source.
• d.c – battery
• a.c - mains.
10. If a heater uses 1500 J of energy
each second, What current will it draw
if it is working from the mains voltage?
•V = 230V
• P = 1500W as P = E / t
•I = P ÷ V
= 1500 ÷ 230
= 6.5 A
11. Calculate the current in a circuit if
135 charges take 3minutes to travel
through the circuit.
•Q=It
t = 3x60 =180s
I = Q/t
• I = 135/180
• I = 0.75A
12. What are the values of the voltage
and frequency of the mains supply?
•230V
•50Hz
13. What is current?
•The rate of flow of
electric charges
around a circuit.
•The charge per second
that passes a point.
14. What are the units for charge?
• Coulombs, C
15. Describe how electrons move in ac
and dc.
• dc electrons move from
negative to positive.
•Ac electrons vibrate
backwards and forwards,
changing direction
16. What danger is present when
using a multiway adapter?
•If too many appliances
are used or ones which
require much current
are used it may
overheat and catch fire.
17. Calculate the number of electrons that pass
through a wire carrying a current of 2 A for
5 s.
Qelectron = 1.6x10-19 C
• Q = It
•
=2x5
•
= 10C
No. of electrons
=10 ÷ 1.6x10-19
= 6.25 x 1019
18. What type of current
is shown by the waveform?
• a.c / alternating
current
19. Why must the fuse value be greater
than the current used by the appliance?
• It melts when it’s
rating/value has been
reached. So in normal
use it does not melt
but if something goes
wrong it melts before
20. What fuse should be used in a
2kW kettle, 3A or 13A?
Show working.
• I=P/V
• I=2000/230
• I=8.7A
• 13A fuse.