Open the simulation Print this page on A4.

Student worksheet

2. D.C. Circuits

Name:

Class: ______ Date: ________

Open the simulation and work through each chapter. Write your prediction before you run the test.

a. Series circuits

Predict

A₁ reads 0.20 A. Predict the reading on A₃ (after both resistors).

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

R₁ / Ω	R₂ / Ω	I / A	V₁ / V	V₂ / V	V₁ + V₂ / V

Pattern I found:

Challenge

Make the ammeter read 0.25 A using the 6.0 V battery and 12 Ω lamps. Fill the gap in the top wire.

My solution

Exam practice

Three identical lamps are connected in series to a 9.0 V battery. What is the p.d. across each lamp? [1]
A 1.0 V
B 3.0 V
C 9.0 V
D 27 V
Answer: ____
A 4.0 Ω resistor and an 8.0 Ω resistor are connected in series to a 12 V supply. Calculate the current. [2]
For the same circuit, calculate the p.d. across the 8.0 Ω resistor. [1]

b. Parallel circuits

Predict

Switch S is opened. Predict what happens to A₁ (lamp branch) and to the main ammeter A.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

R / Ω	A₁ / A	A₂ / A	A / A	A₁ + A₂ / A

Pattern I found:

Challenge

Make the main ammeter read 1.50 A by adding 12 Ω lamps. Drop each lamp so that its two ends sit on the two vertical wires.

My solution

Exam practice

Two lamps of different resistance are connected in parallel to a 6.0 V supply. What is the p.d. across each lamp? [1]
A 3.0 V across each
B 6.0 V across each
C 12 V across each
D It depends on each lamp’s resistance
Answer: ____
The current from the supply to two parallel branches is 0.90 A. The current in one branch is 0.35 A. Calculate the current in the other branch. [1]
A 3.0 Ω resistor and a 6.0 Ω resistor are connected in parallel to a 6.0 V battery. Calculate the current from the battery. [2]

c. Effective resistance

Predict

One 12 Ω resistor: ammeter reads 0.50 A. A second 12 Ω resistor is added in parallel. Predict the new reading.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

Branches	R values / Ω	I / A	R_eff measured / Ω	R_eff calculated / Ω

Pattern I found:

Challenge

Using only 10 Ω resistors, complete the circuit so that the ammeter reads 0.40 A. Join the open end of the top wire to the open end on the right.

My solution

Exam practice

Calculate the effective resistance of a 6.0 Ω resistor and a 3.0 Ω resistor connected in parallel. [2]
Two identical lamps are connected in parallel across a battery. A third identical lamp is connected in parallel with them. What happens to the effective resistance of the lamps and to the current from the battery? [1]
A Resistance increases; current decreases
B Resistance decreases; current increases
C Resistance decreases; current decreases
D Resistance stays the same; current increases
Answer: ____
Two 6.0 Ω resistors are connected in parallel, and this pair is connected in series with a third 6.0 Ω resistor. Calculate the effective resistance. [2]

d. Potential dividers

Predict

R₁ = R₂ = 1.0 kΩ across 9.0 V. Predict Vout when R₂ becomes 2.0 kΩ.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

R₁ / Ω	R₂ / Ω	Vout measured / V	R₂/(R₁+R₂) × 9.0 V

Pattern I found:

Challenge

Set R₁ and R₂ so that V_out = 3.0 V and the battery supplies a current of 1.0 mA.

My solution

Exam practice

A 2.0 kΩ resistor and a 4.0 kΩ resistor are connected in series across a 12 V supply. Calculate the p.d. across the 4.0 kΩ resistor. [2]
In a potential divider, V_out is taken across R₂. Which change increases V_out? [1]
A Increasing R₁
B Increasing R₂
C Decreasing the supply p.d.
D Decreasing R₂
Answer: ____
A 6.0 V supply is connected across R₁ = 3.0 kΩ in series with R₂. What value of R₂ gives 2.0 V across R₂? Give your answer in kΩ. [2]

e. Sensing circuits

Predict

Thermistor at the bottom of the divider. Predict what happens to Vout as it is heated from 20 °C to 80 °C.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

θ / °C or light / %	R_sensor / Ω	Vout / V	Output ON/OFF

Pattern I found:

Challenge

Design a fire alarm: the output must be ON at 60 °C and OFF at 30 °C. Choose where the thermistor goes and the value of the fixed resistor.

My solution

Exam practice

The light shining on an LDR becomes brighter. What happens to its resistance? [1]
A It increases
B It decreases
C It stays the same
D It increases, then decreases
Answer: ____
An NTC thermistor is the lower resistor of a potential divider and V_out is taken across it. The temperature rises. What happens to V_out? [1]
A It rises
B It falls
C It stays the same
D It becomes equal to the supply p.d.
Answer: ____
An LDR is connected in series with a 2.0 kΩ resistor across a 6.0 V supply. In the dark the LDR has a resistance of 10 kΩ. Calculate the p.d. across the LDR. [2]