Predict nuclear emission deflection in an electric field
Use charge sign to distinguish alpha beta-minus and gamma paths between labelled plates.
Exam scope and assessment notes
Extended only (Supplement) · Physics 0972, 2026–2028. Use labelled nuclides, supplied count intervals and stated background conditions. Model drawings are not to scale. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Read plate electric-field direction.
- Identify the emission charges.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
A beta-minus particle enters a downward electric field. Which force direction follows?
What you will learn
- Use charge sign to distinguish alpha beta-minus and gamma paths between labelled plates.
- Apply charge sign to electric deflection in one labelled reference frame.
Read the field and charges
Between a positive upper plate and a negative lower plate, the central electric field points downward. A positive alpha particle experiences downward force toward the negative plate; a negative beta-minus particle experiences upward force toward the positive plate. Uncharged gamma has no electric deflection in this simple model.
The force direction follows charge sign and field direction, not the name of a drawn colour. Reversing plate polarity reverses the charged-particle forces. Keep the same viewpoint and initial rightward motion when comparing the two diagrams.
Separate direction from path size
A field-force direction tells the initial deflection sense, but quantitative bending depends on particle properties, speed, field and path length. Opposite charges do not establish equal curvature. Typical beta paths may bend much more than alpha paths, but the sign comparison alone does not quantify that difference.
The schematic selects rays moving through a uniform central field and does not depict random source directions or a complete beam apparatus. Edge fields, scattering and other interactions are outside the stated simple comparison. Gamma continuing straight means no electric force from its zero charge here, not an absence of every possible material interaction.
Pause and explain
Does opposite deflection establish equal alpha and beta path curvature?
Worked example
Rightward alpha, beta-minus and gamma enter a downward central electric field. Give initial deflections.
Show the worked solution
- Alpha is positive and force follows the field down.
- Beta-minus is negative and force is upward.
- Gamma is uncharged and undeflected by this field.
Answer Alpha down; beta-minus up; gamma undeflected.
Try a topic test
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Find alpha deflection between positive upper and negative lower plates.
Give me a hint
Use the force on a positive charge.
Compare my reasoning
- Field points downward.
- Alpha is positive.
- Its initial force is downward.
Downward, toward the negative plate.
Look for these in your work
- Read the labelled field.
- Use positive alpha charge.
Reverse both plate polarities and state beta-minus force direction.
Give me a hint
Find the new field before applying the negative charge.
Compare my reasoning
- Field now points upward.
- Beta-minus charge is negative.
- Its force is downward.
Downward, toward the new positive lower plate.
Look for these in your work
- Retain the fixed view.
- Reverse only the stated field.
Gamma continues straight in the supplied electric-field diagram. Does this prove it never interacts with matter?
Give me a hint
Distinguish field response from material interaction.
Compare my reasoning
- Gamma has zero electric charge.
- It has no electric deflection in this model.
- Absorption and scattering in matter remain possible.
No; no electric deflection does not exclude material interactions.
Look for these in your work
- Name the model limit.
- Do not turn one absent effect into universal non-interaction.
Common mistakes
- Read plate polarities.
- Use beta-minus charge sign.
- Direction does not determine equal curvature.
What can you explain now?
Which way does electric field point between labelled plates?
Compare with the explanation
From positive to negative
Electric field direction is defined by the force on a positive test charge.
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Make it stick
Apply charge sign to electric deflection in one labelled reference frame.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.