Transcript Slide 1 - hsheldon

Why doesn't electricity just flow out of a wire into the air
around it? Try to explain using scientific terms.
Electric Current Review
Which of the signs below would indicate the most danger?
DANGER!
HIGH RESISTANCE
1,000,000 Ω
DANGER!
HIGH VOLTAGE
1,000,000 V
A
HIGH CURRENT
1,000,000 A
B
DANGER!
HIGH ELECTRIC
POTENTIAL
D
A) “A”
DANGER!
B) “B”
C
DANGER!
HIGH ELECTRIC
FIELD
E
C) “C”
D) “D”
E) “E”
Electric Current Review
How does a battery work?
A) It pulls protons from a large negative charge and puts them back
on a large positive charge.
B) It pulls protons from a large positive charge and puts them back
on a large negative charge.
C) It pulls electrons from a large negative charge and puts them back
on a large positive charge.
D) It pulls electrons from a large positive charge and puts them back
on a large negative charge.
E) None of the above explain how a battery works.
Electric Current Review
Why does a circuit stop conducting when you cut the wire?
A) The current of the circuit becomes infinite.
B) The current of the circuit becomes zero.
C) The resistance of the circuit becomes infinite.
D) The resistance of the circuit becomes zero.
E) The voltage of the circuit becomes infinite.
Electric Current Review
Why don’t birds get electrocuted when they stand on power lines?
A) They don’t offer a potential difference for the current.
B) Birds do get electrocuted. They’re just really tough.
C) Current only flows through metal and birds aren’t metal.
D) Their resistance is too high for the current to flow.
E) Electricity doesn’t actually move through power lines.
Electric Current Review
Why can dropping a plugged-in toaster in the bathtub kill you?
A) Electricity keeps flowing out of the toaster until the water is “full”.
B) Electrons in the toaster combine with those in the water to get high current.
C) When skin is wet, resistance goes down, so the current increases.
D) It can’t kill you. There’s just not enough electricity to kill.
E) The current heats up the water super fast and you burn to death.
Electric Current Practice Problems
1) Why are electrons, rather than protons, the principal charge classwork
carriers in metal wires?
2) Calculate the current in a toaster that has a heating element of 15
Ω when connected to a 120 V outlet.
3) Calculate the current that moves through your fingers (resistance
1000 Ω when you touch them to the terminals of a 6 V battery.
4) If 10 A of current pass through a 90 Ω heating element, what’s
the voltage through the circuit?
5) Consider a circuit with a main wire that branches in two. If the
current is 9 A before the split, what is the current in each branch
if one branch is twice as thick as the other?
 A 1-mile long copper wire has a resistance of 10 Ω. What will be
it’s new resistance when it is shortened by cutting it in
half? What
if we just fold it over in half to get the same
amount of wire in half the distance?

Does an electrical wire have an overall positive or negative
charge? Explain your answer.
Exit Question #11
Imagine we have a gap in a wire like shown below. What can we
say about the point where we have the gap?
a) the current is zero
b) the current is infinite
c) the resistance is zero
d) the resistance is infinite
e) “B” and “C”
f) “A” and “D”