What does an ECG detect and record, and how are the signals obtained from the body?

An ECG detects and records the electrical activity of the heart using electrodes placed on the skin surface.

Where are ECG electrodes typically positioned on the body, and what do they detect?

Electrodes are placed at specific positions on the limbs and chest to detect potential differences caused by the depolarisation and repolarisation of cardiac muscle.

What is the typical order of magnitude of the electrical signals detected by ECG electrodes?

The signals are very small, of the order of millivolts.

Why must the electrical signals from ECG electrodes be amplified?

Because the signals are very small (millivolts) and require amplification before they can be displayed.

What does an ECG machine actually measure between its electrodes?

The ECG machine measures the potential difference between pairs of electrodes.

How do different electrode combinations affect what an ECG shows?

Different electrode combinations provide different views of the heart's electrical activity.

AQA A-Level Physics 7408

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Medical Physics

Simple ECG machines and the normal ECG waveform

3 things to know
Paper 3, section B

Overview

Detecting and amplifying the heart's electrical signal, and the P, QRS and T features.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What does an ECG record, how large are the signals, and why must they be amplified?

Process

What do the QRS complex and the T wave represent, and why is the QRS larger?

Key term

State the correct order of the main features in a normal ECG waveform

Questions from this subtopic

Each one with the model answer underneath.

1
What does an ECG detect and record, and how are the signals obtained from the body?
Model answer
An ECG detects and records the electrical activity of the heart using electrodes placed on the skin surface.
2
Where are ECG electrodes typically positioned on the body, and what do they detect?
Model answer
Electrodes are placed at specific positions on the limbs and chest to detect potential differences caused by the depolarisation and repolarisation of cardiac muscle.
3
What is the typical order of magnitude of the electrical signals detected by ECG electrodes?
Model answer
The signals are very small, of the order of millivolts.
4
Why must the electrical signals from ECG electrodes be amplified?
Model answer
Because the signals are very small (millivolts) and require amplification before they can be displayed.
5
What does an ECG machine actually measure between its electrodes?
Model answer
The ECG machine measures the potential difference between pairs of electrodes.
6
How do different electrode combinations affect what an ECG shows?
Model answer
Different electrode combinations provide different views of the heart's electrical activity.

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