Teach lesson
Three lights, independent branches
Test what happens to one LED branch when other branches share its supply.
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Learning Outcomes
Compare the green branch current with one, two and three parallel branches.
Explain branch independence and distinguish branch current from total current.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Does an extra light take something away?
5 min
Imagine adding another indicator to a control panel. Will the first one lose current because it now has to “share”? Hive lets you compare a green LED alone, green plus red, and all three colours. Each branch has its own 1 kΩ resistor; all branches connect between the same supply and ground.
At a fixed 5 V, predict what adding red and yellow branches will do to the current in the green branch. Explain your reasoning.
Add branches, keep the same measurement
22 min
Read the circuit
The lab button opens a wired circuit on real equipment. A branch is one path containing a resistor and an LED. The LED has an anode (A) and cathode (K); their orientation is already set. Select the DC Power tab to read or change the positive supply setting; select Multimeter to read the voltage. Click Perform Measurement after every change and wait for the result and rack photographs to refresh. Changing a setting alone does not produce a new result. To adjust voltage with the keyboard, focus the voltage knob: Left/Right changes the step; Up/Down changes the value. Check the displayed voltage before measuring.
The multimeter reads the voltage across the resistor, called $V_R$. Record VDC in volts; divide an mV reading by 1,000. For example, 240 mV = 0.240 V. If the display shows uV (microvolts, µV), divide by 1,000,000: 300 uV = 0.000300 V. For a 1 kΩ resistor, $I\,\text{(mA)}=V_R\,\text{(V)}$. This calculates current from measured voltage and the stated resistance.
Use the camera photographs for observations of the real lights. The drawing’s Estimated glow is an illustration of the last result, not a light measurement; turn it off during camera comparisons. A light hidden by glare is unclear, not necessarily off. The rack also contains status lights. If the circuit LED is unclear, keep the same circuit and voltage and press Perform measurement again. Wait for the result and camera photographs to refresh, then inspect the LED again. Briefly note the first and repeat readings and any change in visibility in your written answers; use the repeat result in the table. If the LED is still unclear, choose Unclear; do not judge it from another light or keep repeating until you obtain the answer you expected.
Read the equipment name shown under each result: successive measurements can use different physical Hives. Small differences may therefore reflect different components. A result labelled as a previous recording is not an independent new measurement.
Keep the circuit protected
Keep the supplied wiring and resistors in place. Use only the positive 0–5 V supply, between 1 and 5 V in this activity. Do not connect an LED directly to the supply. Leave the other supplies and function generator unchanged. The meter is already connected across a resistor: leave it in DC voltage mode, never current or resistance mode.
Read the voltage across the resistor to calculate the current through that branch. A and K identify the LED terminals.
Trace one complete branch from supply to ground. The voltmeter connects only to the green resistor.
Changing circuits
When you finish a circuit, use Leave now in Hive, then return to this activity before opening the next lab button. Each button loads its own circuit; do not reuse a previous circuit or rewire the meter.
Green only
Green only
Confirm 5 V and leave the meter across the green branch’s 1 kΩ resistor. Measure, complete the Green only row and leave Hive.
Available in a class session
Green + red
Green + red
Confirm 5 V and leave the meter across the green branch’s 1 kΩ resistor. Measure, complete the Green + red row and leave Hive.
Available in a class session
Green + red + yellow
Green + red + yellow
Confirm 5 V and leave the meter across the green branch’s 1 kΩ resistor. Measure, complete the Green + red + yellow row and leave Hive.
Available in a class session
Repeat green only
Repeat green only
Open this final circuit at 5 V, measure the green resistor again and complete Green only, repeat. Check the equipment name: this may be a different physical Hive.
Available in a class session
Results
Use four rows, always at 5 V. The meter measures only the green branch resistor in every circuit. Enter V_R in V and I_green in mA (same numerical value with 1 kΩ). Observe the green LED, not combined rack brightness. Use the final repeat button for the last row; leave extra rows blank.
| Circuit | Green resistor voltage V | Green branch current mA | Green LED in camera |
|---|---|---|---|
Separate branch and total current
13 min
Subtract the first green-only current from the three-colour green current. Give the signed difference in mA and show the two readings used.
Did adding branches substantially change the green branch current? Use the three configurations and the repeat to explain what your evidence supports.
Answer in writing without changing the circuit: does this meter reading give the total current supplied to all three branches? Explain which current it gives and what extra measurements would be needed to find the total.
What would you check before blaming an extra branch for a small difference between runs?
Submit
After all measurements, leave Hive and return here. Mark the lab practice as done, check every results row and required answer, then submit the activity.
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