Lesson 14: Current in Series Circuit

d. series A series circuit is one in which there is only one path for current to flow.

A circuit having only one current path is called a(n) ? circuit. a. capacitive b. inductive c. parallel d. series

d. rheostat A rheostat is a variable resistor that has 2 terminals. A potentiometer may be used as a rheostat if only 2 of the 3 terminals are used because it does actually adjust the resistance of the circuits.

A two-lead variable resistor used to adjust current in a circuit is called a ? . a. bi-metallic switch b. potentiometer c. regulator d. rheostat

True or False: If the resistance in a circuit is doubled, the current would also be doubled.

False The ratio of resistance to current is inversely proportional.

b. 1.5 A Voltage to current is a directly proportional ratio. Equation to solve for E(R2): R1/R2 = E(R1)/E(R2) 20ohms/60 ohms = 30 V/E(R2) Cross multiply, then divide: 1800 = 20 E(R2) 1800 ÷ 20 = 90 E(R2) = 90 V Solve for total circuit voltage: E(T) = E(R1) + E(R2) = 30 + 90 = 120 V Solve for total circuit resistance: R(T) = R1+ R2 = 20 + 60 = 80 ohm With the found values of total voltage and total resistance, solve for the total circuit current using Ohm's Law. I(T) = E(T)/R(T) = 120 V / 80 ohm = 1.5A

Find the current flow through the following circuit. Begin by using the given resistance values of R1, R2, and the voltage drop across R1 to solve for the voltage drop across R2. Next, find the total circuit voltage. Then, find the total circuit resistance. Use Ohm's Law and the found total voltage and resistance to solve for the total circuit current. a. 0.66 A b. 1.5 A c. 2 A d. 3 A

a. ammeter

In order to measure current, the ? must be placed in series with the component for which the current is to be measured. a. ammeter b. ohmmeter c. voltmeter d. wattmeter

d. total voltage and total resistance of

In order to solve for total current in a series circuit using Ohm's Law, the ? the circuit must be known. a. individual resistor values in b. individual voltage drops in c. total power consumed by d. total voltage and total resistance of

b. 1.25 A As shown: I = E ÷ R = 30 ÷ 12 = 2.5 A After switching: I = E ÷ R = 30 ÷ 24 = 1.25 A

In this circuit, the SW1 switch is closed and the SW2 switch is in the open position. As shown, the ammeter reading is 2.5 amperes. If the SW1 switch is opened and the SW2 switch is closed, the ammeter reading will be ? . a. 0 A b. 1.25 A c. 2.5 A d. 5 A

c. ohm

Ohm's Law states that it takes one volt to push one ampere through one ? . a. farad b. henry c. ohm d. watt

a. current

The ? is the same at any point of a series circuit. a. current b. resistance c. voltage d. wattage

d. 1.25 A RT = R1 + R2 + R3 RT = 20 + 40 + 100 = 160 Ω IT = ET ÷ RT = 200 ÷ 160 = 1.25 A

The current flow through the circuit components is ? . a. 0.25 A b. 0.75 A c. 1 A d. 1.25 A

b. 0.14 mA The scale nearest the bottom corresponds to the 0-0.5 DCmA scale, and is calibrated in 0.02-DCmA (or 20 microampere) increments.

The selector is in the 0.5 DCmA position. Indicate the correct current value. a. 0.10 mA b. 0.14 mA c. 0.71 mA d. 0.80 mA

c. 0.5 mA The scale nearest the bottom corresponds to the 0-0.5 DCmA scale, and is calibrated in 0.02-DCmA (or 20 microampere) increments.

The selector is in the 0.5 DCmA position. Indicate the correct current value. a. 0.15 mA b. 0.25 mA c. 0.5 mA d. 5.0 mA

d. 19.5 mA The scales for current on the analog meter are located at the bottom of the meter face. The scale nearest the bottom corresponds to the 0-0.5 DCmA scale, and is calibrated in 0.02-DCmA (or 20 microampere) increments. The scale just above this scale is the 0-25 DCmA scale. The 25-DCmA scale is calibrated in 1-DCmA increments. The scales used for current measurements are much more linear than the scale used earlier for resistance measurements, and for this reason it is much easier to read close to the ends of the scale. However, maximum accuracy is still obtained when the meter is read with the indicator near the center of the selected current scale.

The selector is in the 25 DCmA position. Indicate the correct current value. a. 2 mA b. 4.78 mA c. 15 mA d. 19.5 mA

d. overload As with the resistance scales, an overcurrent or current larger than the selected scale would be displayed with a single "1" digit. Care must be taken not to confuse the overcurrent indication "1. ," "1 . ," or "1 . " with a valid reading such as "1.000," "1.00," "10.00," or "100.0." Some digital meters indicate such an overload condition by displaying the letters "OL." Read the manual supplied with any meter to find out how that meter indicates overcurrent or overload conditions.

The selector is in the 2A position. Indicate the correct current value. a. 100 mA b. 0.1 A c. 1.0 A d. overload

b. 0.25 mA

The selector is in the 2mA position. Indicate the correct current value. a. 0.025 mA b. 0.25 mA c. 2.5 mA d. 25 mA

b. resistance

The total amount of resistance to current flow in a series circuit is equal to the sum of the ? in that circuit. a. current b. resistance c. voltage d. wattage

True

True or False: A fuse is a safety device placed in a circuit to limit the amount of current that can flow in the circuit.

True A potentiometer is a variable resistor that has 3 terminals. Potentiometers are generally used to adjust the voltage applied to a circuit.

True or False: A variable resistor wired as a potentiometer has three leads.

False An increase in the total resistance of a circuit would cause a decrease in the current in that circuit.

True or False: An increase in the total resistance of a circuit would cause an increase in the current in that circuit.

False Decreasing the applied voltage to a circuit would cause the current to decrease.

True or False: Decreasing the applied voltage to a circuit would cause the current to increase.

False Current to voltage is directly proportional. Current to resistance is inversely proportional.

True or False: In a DC circuit, the current is inversely proportional to the voltage, and directly proportional to the resistance.

True I = E/R

True or False: In a series circuit, the total current is equal to the total voltage divided by the total resistance.

True

True or False: Since there is only one current path through a series circuit, the same current must flow through every component.

True Please make note of subscripts (IT = total current) that are often used in electrical formulas to properly identify which components are being referenced.

True or False: Subscripts allow precise communication about various components of a circuit.

True

True or False: The basic Ohm's Law algebraic formula for current is: I = E/R

False Generally the meter's selector switch can be set to the highest scale, and then adjusted downward if the scale is too high.

True or False: When measuring current in a circuit, the meter should always be set on the lowest current scale before performing the measurement.

True When measuring current with either type of meter, the procedure to obtain accurate measurement of the value of the current is the same. As with resistance, digital meters often are easier to read and more precise for steady-state currents, or currents that are not rapidly changing; while analog meters often work better when currents are changing or varying and will not settle down to a precise value.

True or False: When the current level is continuously changing in a circuit, an analog meter should be used.

a. 55 Ω RT = ET ÷ IT = 240 ÷ 3 = 80 Ω R1 + R2 = RT 25 + R2 = 80 Ω 25 + R2 - 25 = 80 - 25 R2 = 55 Ω

Use the given voltage and current values to find the total circuit resistance. With the found total resistance, calculate the resistance value of R2. a. 55 Ω b. 65 Ω c. 80 Ω d. 695 Ω