NAME________________ Some Practice Electricity Questions:

Describe the steps in using coal to make electricity that comes to your house and makes your stove oven work. (an oven has heating coils, a fan, and a light).

__Coal (chemical)__*à*__heat
(some lost) __*à*__ water
__*à*__
steam (mechanical) __*à*__
turbine (mechanical, some lost to friction) __*à*__
magnet turns -__*à*__
(mechanical) -__*à*__
induces electricity in coil of wire (electrical, around 76% efficient)--__*à*__
transmitted (some lost to heat due to resistance) -__*à*__
house (transformer steps down the voltage) -__*à*__
house __*à*__
oven (heat) and fan (mechan) and light (light)__

What are the things that might change the: current, voltage, power, of the oven?

__Current can be changed by adding resistance to
lessen the current, voltage can be transformed by a transformer, and power will
be change by current OR voltage__

If an object has a -1 Charge it:

A)
has one electron B)
has 10^{19} electrons

**C)
has 10^{19} extra electrons** D)
has -10

Describe the difference in how electrons travel in a wire in DC and AC current:

__Electrons in a DC current travel mostly in one
direction, while in ac, they travel back and forth.__

If electricity is like gravity, what are the similarities?

Mass *Charge*

G (gravitational acceleration) *Field*

Field

Potential Energy *Voltage*

Work

What are the differences?* Main one is that electricity
can be positive or negative, so attractive or repulsive… gravity that we deal
with on earth has a constant field (because the distances are so great), but
electric fields change with distance.*

-------------------------

If two charges are moved twice as far apart, how does the
force change? * IT is a fourth
as less (inverse square law)*

If my light is 100 Watts, and is attached to my house, which
is 120 V, what is the typical current in the bulb?

* Current
is Power/Voltage = 100/120 =
0.83333 Amps*

I have a device that uses 12 V of 300 mA (.3 Amps) current.
What is the amount of energy it uses in 10 seconds? How much charge flows in 10
seconds? What is the current arriving into the device, and how is it changed?

*Power = Voltage*Current = 12 * 0.3 = 3.6 Watts = 3.6
Joules/sec * 10 sec = 36 Joules*

*If it is plugged into a 120 Volt house current, that
means that the voltage has been decreased by 10 times, so it really takes in 30
Amps of current. Changed by a transformer*

A flashlight bulb with a potential difference of 4.5 V has a
resistance of 8 ohms. How much current is in the bulb filament? How much power
does it use?

* Voltage =
Current * Resistance. Current = Voltage/Resistance =4.5/8 = 0.5625 Amps.*

*Power = Current * Voltage = 0.5625*4.5=2.53 Watts*

If a light bulb has a resistance of 240 ohms when operating
at 120 V, what is the current in the light bulb? What is the effective power
use of the bulb? If the bulb is one for 1 second, how much energy is lost?
Where did it go?

*Voltage = Current * Resistance, 120 = 240*I, I=
120/240 = 0.5 Amps,*

* Power =
Current* Voltage = .5 * 120 = 60 Watts = 60 Joules/sec * 1 sec uses 60 Joules
that is given off as heat. *

If a 325 Watt heater has a current of 6 Amps, what is the
resistance of the heating element?

*Power = Current * Voltage , 325 = V (6), voltage =
325/6 =54.17 Volts*

*Voltage = Current * Resistance, 54.17 = 6 * R , R =
9.03 ohms*

* *

What does the electric company charge you for?

A) Power (watts) B)
Current (amps) D)
Voltage (voltage) *E)
Energy (KW HRs)*

Explain why you might want to wire your house using parallel
circuits, not series.

*In a series circuit if one device goes, the current is
not passed on, but in a parallel circuit, like a stream dividing, if one path
is blocked, the flow continues along the other paths.*

A 12 Volt battery is used to power a light bulb. There are
three resistors in series, 18 ohms, 24 ohms, and 8 ohms in the circuit before
the light bulb. Draw a diagram, and calculate the current through the bulb, and
its power use.

*Resistance= 18+24+8= 50 ohms*

*Voltage= Current * Resistance*

*12 = I * 50, Current = I= 12/50= .24 ohms*

* *

If you connected a toaster of 1200 Watts, a coffee pot of
750 Watts, and a microwave at 600 Watts to a house (120 V), how much current
would they all draw if on at the same time?

*They would all be in series, so the total power would
be 1200+750+600=2550 Watts*

*Power = Current * Voltage, 2550 = I * 120 I =
2550/120=21.25 Amps*

A 12 Volt battery is connected to resistors (10 ohms and 20 ohms) in parallel.

Draw a diagram

What is the voltage in each resistor?

*1) Voltage is 12 V, 2)
Voltage is 12 V*

What is the current in each resistor?

*1) Resistance = 10 ohms, Voltage = 12 V, I = V/R=12/10
= 1.2 Amps*

*2) Resistance = 20 ohms, Voltage = 12 V, I =V/R=12/20
= 0.6 Amps*

What is the total current?

*Total current is the two added together, 1.2 + 0.6 =
1.8 Amps*

What is the total resistance?

*Voltage = 12 V, Current = 1.8 Amps,*

*R = V/I = 12/1,8 = 6.67 ohms (less than each one!)*

*OR
1/Rtot = 1/R1 + 1/R2
1/Rtot = 1/10 + 1/20 = 3/20 , Rtot = 20/3 = 6.67 ohms*

Describe three ways to use magnetism and wire to make a
current:

*Move the magnet near the wire, move the wire near the
magnet, move both!*